DATASTRUCTURES

Table of Contents

No.	Questions
1	Data Structure
2	Algorithm
3	Time Complexity
4
5
7
8
9
10
101	Even or Odd
102	Multiplication table
103	Sum of first n Natural Numbers
104	Swap two numbers
105	Closest number divisible by m
106	Dice Problem
107	Simple Interest
108	Area of a Circle
109	Sum of the digits of a given number
110	Prime Number
111	Exactly 3 divisors
112	Check if a number is a power of another number
113	Factorial of a Number
114	Square root of an integer
115	Find GCD or HCF of Two Numbers
116	Find LCM of two numbers
117	Jumping Numbers
118	Perfect Number
119	Add two fractions
120	Fraction to Recurring Decimal
121	Find Recurring Sequence in a Fraction
122	Find Sum of even and odd elements in an array
123	Decimal to Binary Conversion
124	Calculate distance between two points
125	Armstrong Numbers
126	Maximum and minimum of an array
127	Array Reverse
128	Cyclically rotate an array by one
129	Array Sorting
130	Duplicate elements in an array
131	Find distinct values from array
132	Count number of occurrences (or frequency) in a sorted array
133	Dutch National Flag Problem
134	Balanced Brackets
135	Largest number in Array
136	Count vowels in a string
137	Nested Array
138	Reverse a String
139	Chain Calculator
140	Remove Duplicates from an Array
141	Check if Prime number
142	Fibonacci Series
143	XYZ
144	XYZ
145	XYZ
146	XYZ
147	XYZ
148	XYZ
201	Check for Binary
202	Camel Case Conversion
203	Binary Substrings with Corners as 1s
204	Check for Panagram
205	[Check for Palindrome] (#)
206	[Check for Substring] (#)
207	[Check for Subsequence] (#)
208	[Check for Anagrams] (#)
209	[Check for K-Anagrams] (#)
210	[Duplicates in a String] (#)
211	[Longest Substring Between Equals] (#)
212	[Left Rotate] (#)
213	[Check for Rotation] (#)
214	[Validate an IP address] (#)
215	[Count strings with consecutive 1’s] (#)
216	[Generate all binary strings from given pattern] (#)
217	[Smallest and Largest Word in a String]
218	[Count number of equal pairs in a string]
219	[Second most repeated word in a sequence]
220	[All strings by placing spaces]
221	[Sort string of characters]
222	[Char Frequencies in Order of Occurrence]
223	[Char Frequencies in Alphabetical order]
224	[URLify a String]
225	[First Repeating Character]
226	[First Non-Repeating Character]
1	[K’th Non-repeating Character]
1	[Implement atoi]
1	[Add 2 Binary Strings]
1	[Add n Binary Strings]
1	[Multiply 2 Strings]
1	[Divide large number]
1	[Isomorphic Strings]
1	[Remove Adjacent]
1	[Roman to Integer]
1	[Interleaved Strings]
1	[Permutations of a String]
1	[Longest Palindromic Substring]
1	[Queries for characters in a repeated string]
1	[Count anagram substrings]
1	[Count binary strings without consecutive 1’s]
1	[Lexicographically next string]
1	[Split String into four distinct strings]
1	[Word Break Problem]
1	[Length of Longest Balanced Subsequence]
1	[Minimum Swaps for Bracket Balancing]
1	[String to mobile numeric keypad sequence]
1	[Minimum number from given sequence]
1	[Shortest path to print a string on screen]
1	[Mirror characters of a string]
1	[Lexicographic Rank of a String]
1	[Multiply Large Numbers]
1	[Ways to increase LCS length of 2 strings by one]
1	[Min rotations required to get the same string]
1	[Find if an array of strings can be chained to form a circle]
1	[Alien Dictionary]
1	[Make two strings Anagram]
1	[Make two Strings Anagram Without Deletion]
1	[Palindrome Substring Queries]
1	[Powet Set in Lexicographic order]
1	[Minimum Word Break]
1	[Word Search - 8 Directions and Straight Movement]
1	[Word Search - 4 Directions and Zig-Zag Allowed]
1	[Minimum number of bracket reversals needed to make an expression balanced]
1	[Word Wrap problem ( Space optimized solution )]
1	[Decode a string recursively encoded as count followed by substring ]

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1. What is a Data Structure?

A data structure is a specialized way of organizing, managing, and storing data so it can be accessed and modified efficiently.

Types of Data Structures

1. Linear Data Structures: Data is arranged sequentially.

• Array: Collection of elements stored at contiguous memory locations.
• Linked List: Elements (nodes) are connected using pointers.
• Stack: Follows the LIFO (Last In, First Out) principle.
• Queue: Follows the FIFO (First In, First Out) principle.

2. Non-Linear Data Structures: Data is arranged hierarchically or graphically.

• Tree: Hierarchical structure with a root node and child nodes (e.g., binary tree).
• Graph: Collection of nodes (vertices) connected by edges.
• Heap: Specialized tree-based data structure.

3. Hash-Based Structures:

• Hash Table/Map: Stores key-value pairs for quick lookups.

4. Other Advanced Structures:

• Trie: Used for efficient string searching.
• Disjoint Set (Union-Find): Used for dynamic connectivity problems

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2. What is an Algorithm?

An algorithm is a step-by-step procedure or formula for solving a problem. It takes input, processes it, and produces output.

Characteristics of a Good Algorithm

• Correctness: Produces the right result for all valid inputs.
• Efficiency: Minimizes the use of computational resources (time and space).
• Clarity: Easy to understand and implement.
• Scalability: Performs well as the size of the input increases.

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3. Time Complexity

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101. Check Even or Odd

const input = 11
console.log("Is the number even ?", isEvenOrOdd(input))

function isEvenOrOdd(num){
    console.log(num)
    if(num %2 == 0 ){
        return "Even"
    }else{
        return "Odd"
    }
}

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102. Multiplication Table

    const tableUpto = 10;
    const tableOf = 7;
    multiplicationTable(tableOf, tableUpto);

    function multiplicationTable(tableOf, tableUpto){
        for(let i=1; i<=tableUpto; i++){
            console.log(tableOf , " x ", i , " = " ,tableOf * i)
        }
    }

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103. Find Sum of first n Natural Numbers

    function findSum(n)
    {
    let sum = 0;
    for (let x = 1; x <= n; x++) 
        sum = sum + x;
    return sum;
    }

    let n = 5;
    console.log(findSum(n));

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104. How to swap two numbers without using a temporary variable?

    let x = 10;
    let y = 15

    swapNumbers(x,y);

    function swapNumbers(i,j){
        console.log("Numbers before : ",  i , "  " , j)
        let temp = 0;
        temp = i;
        i = j;
        j = temp;
        console.log("Exchanged numbers : ", i , "  " , j)
    }

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105. Find the number closest to n and divisible by m

For ex. num=17 , mul=4. Find a number closest num which is multiple of mul. Answer should be 16.

let num = 19;
let mul = 4;
const closest = closestNumber(num, mul)
console.log('Closest number to ', num , "which is multiple of ", mul , " is : ", closest)

function closestNumber(num, multipleOf){
    let remainder = num % mul ; 
    let closer1  = num - remainder;
    let closer2  = num - remainder + mul;
    
    return (num-closer1 < closer2-num)?  closer1 : closer2;
}

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106. Dice Problem

You are given a cubic dice with 6 faces. All the individual faces have a number printed on them. The numbers are in the range of 1 to 6, like any ordinary dice. You will be provided with a face of this cube, your task is to guess the number on the opposite face of the cube.

In a normal 6-faced dice, 1 is opposite to 6, 2 is opposite to 5, and 3 is opposite to 4.

    // 1-6  ,  2-5   ,  3-4

    let input = 5;
    oppositeFaceOfDice(input);

    function oppositeFaceOfDice(n){
            oppositeSide = 7-n ;
            console.log('Opposite side of ', n , ' is : ' , oppositeSide)
    }

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107. Simple Interest

Given Principal p, Rate r and Time t, the task is to calculate Simple Interest.

function simpleInterest(p, r, t) {
    return (p * r * t) / 100;
}

let p = 10000, r = 10, t = 3;
console.log(simpleInterest(p, r, t));

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108. Area of a Circle

    let input = 5;
    areaOfCircle(input);

    function areaOfCircle(n){
        area = Math.PI  *  Math.pow(n,2) ;
        console.log('Area : ' , area)
    }

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109. Sum of the digits of a given number

    let input = 123456;
    sumOfDigits(input);

    function sumOfDigits(num){
        let sum =  0;
        do{
            let remainder = num%10;            
            num -= remainder;                  
            num = num/10;                    
            sum +=remainder
        }while(num>0)
        console.log('Sum : ' , sum)
    }

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110. Check for Prime Number

   const input = 29;

    function isPrime(num){
        if(num<1) return false;
        if(num===2)  return true;
        for(let i =2 ; i<Math.sqrt(num);i++){
            if(num%i === 0) return false;
        }
        return true;
    }

    result=isPrime(input);
    console.log('Is prime ?  ', result)

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111. Find numbers from 1 to N with exactly 3 divisors

Check numbers from 1 to N with exactly 3 divisors Answer should be 16

input = 20;
console.log("Numbers having exactly three divisors:  " , hasThreeDivisors(input))

function hasThreeDivisors(num){
    let numbersDivisibleByThreeDiv = [];
    if(num==1 || num==0){
        return numbersDivisibleByThreeDiv;
    }else if(num>=2){
        for(let i=2; i<num; i++){
            let count = 0;
            for(let j=2; j<i; j++){
                if(i%j == 0 ){
                    count ++;
                }
            }
            if(count==3)  {
                numbersDivisibleByThreeDiv.push(i)
                return numbersDivisibleByThreeDiv;
            }
        }
    }else if(num<= -1){
         for(let i=-2; i>=num; i--){
            let count = 0;
            for(let j=-2; j>i; j--){
                if(i%j == 0 ){
                    count ++;
                }
            }
            if(count==3)  {
                numbersDivisibleByThreeDiv.push(i)
                return numbersDivisibleByThreeDiv;
            }
        }
    }
}

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112. Check if a number is a power of another number

Given two positive numbers x and y, check if y is a power of x or not.

    console.log(isPowerOf(128, 2));
    console.log(isPowerOf(125, 5));
    console.log(isPowerOf(25, 5));
    console.log(isPowerOf(125, 2));

    function isPowerOf(num, powerOf){
        do{
            if(num/powerOf == powerOf) {
                return 'Yes'
            }else{
                if(num % powerOf ==0) {
                    num = num/powerOf 
                }else return 'No'
            }
        }while(num>powerOf)
    }

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113. Factorial of a Number

    console.log(factorial(5))

    function factorial(num){
        let factorial = 1;
        for(let i=num; i>1; i--){
            factorial*= i;
        }
        return factorial;
    }

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114. Square root of an integer

Given a positive integer n, find its square root. If n is not a perfect square, then return floor of √n.

    console.log("Nearest floor square root : ", floorSquareRoot(25))
    console.log("Nearest floor square root : ", floorSquareRoot(29))
    console.log("Nearest floor square root : ", floorSquareRoot(125))
    console.log("Nearest floor square root : ", floorSquareRoot(135))

    function floorSquareRoot(num){
        let result = 0;
        for(let i=1; i<num+1; i++){
            if(i*i == num){
                result = i;
                return result;
            }
            if(i*i > num){
                result= i-1;
                return result
            }
        }
    }

    console.log("Nearest floor square root : ", floorSquareRoot(29))

    function floorSquareRoot(num){
        return Math.floor(Math.sqrt(num));
    }

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115. Find GCD or HCF of Two Numbers

const hcf =  highestCommonFactor(36,72);
console.log(hcf);

function highestCommonFactor(x,y){
    let commonFactors = [];
    let factorsOfX = [];
    let factorsOfY = [];
    let divisor = 2;
    
    do{
        if((x%divisor)==0 && (y%divisor)==0){
            commonFactors.push(divisor)
            x /= divisor;
            y /= divisor;
        }else if((x%divisor)==0){
            factorsOfX.push(divisor)
            x /= divisor;
        }else if((y%divisor)==0){
            factorsOfY.push(divisor)
            y /= divisor;
        }else{
            divisor++;
        }
    }while(x>1 || y>1);
   
    // HCF = multiply all commonFactors 
    let hcf = 1;
    for(let i=0; i<commonFactors.length; i++){
        hcf*= commonFactors[i];
    }
    return hcf;
}

    const commonFactors  = highestCommonFactor(36,72);
    console.log(commonFactors);
    console.log("Highest common factor : ", commonFactors.pop())

    function highestCommonFactor(x,y){
        let lesserNumber = x>y? y : x;
        let commonFactors = [];
        for(let i=2; i<=lesserNumber; i++){
            if(x%i==0 && y%i==0){
                commonFactors.push(i)
            }
        }
        return commonFactors
    }

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116. Find LCM of two numbers

LCM of two numbers is the smallest number which can be divided by both numbers.

    const lcm  = leastCommonMultiple(45,4500);
    console.log("Least common multiple : ", lcm)

    function leastCommonMultiple(x,y){
        let commonFactors = [];
        let uncommonFactors = [];
        let allFactors = [];
        let divisor = 2;            //start with 2
        
        do{
            if((x%divisor)==0 && (y%divisor)==0){
                commonFactors.push(divisor)
                x /= divisor;
                y /= divisor;
            }else if((x%divisor)==0){
                uncommonFactors.push(divisor)
                x /= divisor;
            }else if((y%divisor)==0){
                uncommonFactors.push(divisor)
                y /= divisor;
            }else{
                divisor++;
            }
        }while(x>1 || y>1);
    
        // LCM = commonFactors * uncommonFactors
        allFactors = commonFactors.concat(uncommonFactors);
        console.log("All factors : ", allFactors)
    
        let lcm = 1;
        for(let i=0; i<allFactors.length; i++){
            lcm*= allFactors[i];
        }
        return lcm;
    }

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117. Jumping Numbers smaller than or equal to a given value

A number is called as a Jumping Number if all adjacent digits in it differ by 1. The difference between ‘9’ and ‘0’ is not considered as 1. All single digit numbers are considered as Jumping Numbers. For example 7, 8987 and 4343456 are Jumping numbers but 796 and 89098 are not. Given a positive number x, print all Jumping Numbers smaller than or equal to x. The numbers can be printed in any order.

    console.log('Jumping numbers : ', findJumpingNumbers(20))

    function findJumpingNumbers(num){
        let jumpingNumList = [];
        for(let i=0; i<= num; i++){
            let currentNumTemp = i;
            let currentNum= i;
            if(i<=9){
                jumpingNumList.push(i)
            }else{
                let previousRemainder = currentNum%10 ;
                let isCurrentNumJumping = false;
                do{
                    currentNumTemp -= previousRemainder;
                    currentNumTemp= currentNumTemp/10;
                    currentRemainder= currentNumTemp%10;
                    if((previousRemainder - currentRemainder == 1) || previousRemainder - currentRemainder == -1){
                        isCurrentNumJumping = true
                        jumpingNumList.push(currentNum)
                    }else {
                        isCurrentNumJumping = false;
                    };
                    previousRemainder = currentRemainder;
                }while(currentNumTemp>10);
            }
        }
        return jumpingNumList;
    }

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118. Perfect Number

A number is a perfect number if is equal to sum of its proper divisors, that is, sum of its positive divisors excluding the number itself. Write a function to check if a given number is perfect or not. Eg. 6, 28, 496, 8128, 33550336, 8589869056, and 137438691328 are few perfect numbers.

    let input = 497;
    console.log(isPerfectNumber(input));

    function isPerfectNumber(num){
        let factors = [];
        let divisor = 2;
        do{
            if((num%divisor)==0){
                factors.push(divisor)
                num /= divisor;
            }else{
                divisor++;
            }
        }while(num>1);
    
        // Perfect number is (number == multiply all factors of the number)
        let multiplicationOfFactors = 1;
        console.log(factors)
        for(let i=0; i<factors.length; i++){
            multiplicationOfFactors*= factors[i];
        }
        return input == multiplicationOfFactors;
    }

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119. Add two fractions

Add two fraction a/b and c/d and print answer in simplest form.

Algorithm to add two fractions

Find a common denominator by finding the LCM (Least Common Multiple) of the two denominators. Change the fractions to have the same denominator and add both terms. Reduce the final fraction obtained into its simpler form by dividing both numerator and denominator by their largest common factor.

    num1 = 2;
    den1 = 3;
    num2 = 4;
    den2 = 5;
    console.log(addFractions(num1, den1, num2, den2));

    function addFractions(num1, den1, num2, den2){
        const denominator = leastCommonMultiple(den1, den2)
        num1 = num1*(denominator/den1);
        num2 = num2*(denominator/den2);
        let numerators = num1 + num2;
        let denominators = denominator*2;
        commonFactor = highestCommonFactor(numerators, denominators)
        const newNumerator = numerators/commonFactor;
        const newDenominator = denominators/commonFactor;
        return (newNumerator + " / " + newDenominator);
    }

    function leastCommonMultiple(x,y){
        let commonFactors = [];
        let uncommonFactors = [];
        let allFactors = [];
        let divisor = 2;            
        
        do{
            if((x%divisor)==0 && (y%divisor)==0){
                commonFactors.push(divisor)
                x /= divisor;
                y /= divisor;
            }else if((x%divisor)==0){
                uncommonFactors.push(divisor)
                x /= divisor;
            }else if((y%divisor)==0){
                uncommonFactors.push(divisor)
                y /= divisor;
            }else{
                divisor++;
            }
        }while(x>1 || y>1);

        // LCM = commonFactors * uncommonFactors
        allFactors = commonFactors.concat(uncommonFactors);
        console.log("All factors : ", allFactors)

        let lcm = 1;
        for(let i=0; i<allFactors.length; i++){
            lcm*= allFactors[i];
        }
        return lcm;
    }

    function highestCommonFactor(x,y){
        let lesserNumber = x>y? y : x;
        let commonFactors = [];
        for(let i=2; i<=lesserNumber; i++){
            if(x%i==0 && y%i==0){
                commonFactors.push(i)
            }
        }
        return commonFactors.pop()
    }

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120. Fraction to Recurring Decimal

Given two integers a and b(b != 0), the task is to return the fraction a/b in string format. If the fractional part is repeating, enclose the repeating part in parentheses.

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121. Find Recurring Sequence in a Fraction

Given a fraction, find a recurring sequence of digits if it exists, otherwise, print “No recurring sequence”.

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122. Write a program to print Sum of even and odd elements in an array

Given an array, write a program to find the sum of values of even and odd index positions separately.

    let inputArr = [1, 2, 3, 4, 5, 6]; 
    let sumOfEvenPositions=0;
    let sumOfOddPositions=0;
    separateEvenOddSums(inputArr);

    function separateEvenOddSums(arr){
        for(let i=0; i<arr.length; i++){
            if(i%2==0){
                sumOfOddPositions+= arr[i]
            }else{
                sumOfEvenPositions+= arr[i]
            }
        }
        console.log('sumOfEvenPositions :', sumOfEvenPositions)
        console.log('sumOfOddPositions :', sumOfOddPositions)
    }

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123. Write a program for Decimal to Binary Conversion

Given a decimal number as input, we need to write a program to convert the given decimal number into an equivalent binary number.

For Example:

We are converting Base10 to Base2. If the decimal number is 125 Keep dividing it by 2 and note the remainder. Now collect the remainder from bottom to top. This is binary number.

    console.log(decToBinary(125));

    function decToBinary(num){
        let binaryNumber = 0;
        let powerByPlaceValue = 1;
        do{
            remainder = num%2; 
            num = (num-remainder)/2;
            binaryNumber = binaryNumber + remainder*powerByPlaceValue;
            powerByPlaceValue = powerByPlaceValue*10;
        }while(num>0)
        return binaryNumber;
    }

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124. Write a program to calculate distance between two points

You are given two coordinates (x1, y1) and (x2, y2) of a two-dimensional graph. Find the distance between them.

Eg. Input : x1, y1 = (3, 4) x2, y2 = (7, 7) Output : 5

Input : x1, y1 = (3, 4) x2, y2 = (4, 3) Output : 1.41421

Calculate the distance between two points. We will use the distance formula derived from Pythagorean theorem. The formula for distance between two point (x1, y1) and (x2, y2) is Distance = sqrt{(x2-x1)^{2} + (y2-y1)^{2}}

    function distance(x1, y1, x2, y2) {
        return Math.sqrt(Math.pow((x2 - x1), 2) + Math.pow((y2 - y1), 2));
    }
    console.log(distance(3, 4, 4, 3));

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125. Program for Armstrong Numbers

Given a number x, determine whether the given number is Armstrong’s number or not.

A positive integer of n digits is called an Armstrong number of order n (order is the number of digits) if

abcd... = pow(a,n) + pow(b,n) + pow(c,n) + pow(d,n) + ....

Eg.

Input:153 Output: Yes 153 is an Armstrong number. 111 + 555 + 333 = 153

Input: 120 Output: No 120 is not a Armstrong number. 111 + 222 + 000 = 9

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126. Maximum and minimum of an array using minimum number of comparisons

Given an array of size N. The task is to find the maximum and the minimum element of the array using the minimum number of comparisons.

Examples:

Input: arr[] = {3, 5, 4, 1, 9} Output: Minimum element is: 1 Maximum element is: 9

Input: arr[] = {22, 14, 8, 17, 35, 3} Output: Minimum element is: 3 Maximum element is: 35

   let inputArr = [1, 12, 7, 9, 10, 6]; 

    console.log("Minumum : ", findMini(inputArr));
    console.log("Maximum : ", findMaxi(inputArr));

    function findMini(arr){
        let minimum = arr[0];
        arr.forEach((el)=>
            {
                if(el<minimum)  minimum=el
            }
        );
        return minimum
    }

    function findMaxi(arr){
        let maximum = arr[0];
        arr.forEach((el)=>
            {
                if(el>maximum)  maximum=el
            }
        );
        return maximum 
    }

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127. Array Reverse

Given a fraction, find a recurring sequence of digits if it exists, otherwise, print “No recurring sequence”.

Given an array arr[], the task is to reverse the array. Reversing an array means rearranging the elements such that the first element becomes the last, the second element becomes second last and so on.

Examples:

Input: arr[] = {1, 4, 3, 2, 6, 5}
Output: {5, 6, 2, 3, 4, 1} Explanation: The first element 1 moves to last position, the second element 4 moves to second-last and so on.

Input: arr[] = {4, 5, 1, 2} Output: {2, 1, 5, 4} Explanation: The first element 4 moves to last position, the second element 5 moves to second last and so on.

    let inputArr = [1, 4, 3, 2, 6, 5];
    console.log(reverseArray(inputArr));

    function reverseArray(arr){
        console.log(arr)
        let reversedArray=[];
        for(let i=arr.length-1; i>=0; i--){
            reversedArray.push(arr[i])
        }
        return reversedArray;
    }

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128. Program to cyclically rotate an array by one

Given an array, the task is to cyclically rotate the array clockwise by one time.

Examples:

Input: arr[] = {1, 2, 3, 4, 5} Output: arr[] = {5, 1, 2, 3, 4}

Input: arr[] = {2, 3, 4, 5, 1} Output: {1, 2, 3, 4, 5}

Hint: Assign every element with its previous element and first element with the last element .

    let inputArr = [1, 4, 3, 2, 6, 5];
    let numOfRotations = 1;
    console.log(rotateOnce(inputArr, numOfRotations));

    function rotateOnce(arr, rotations){
        console.log(arr)
        let rotatedArray=[];
        let numOfRotations = rotations;
        rotatedArray.push(arr[arr.length- numOfRotations])
        for(let i=0; i < (arr.length-numOfRotations); i++){
            rotatedArray.push(arr[i])
        }
        return rotatedArray;
    }

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129. Array Sorting

Sorting an array means arranging the elements of the array in a certain order. Generally sorting in an array is done to arrange the elements in increasing or decreasing order.

Problem statement: Given an array of integers arr, the task is to sort the array in ascending order and return it, without using any built-in functions.

Example:

Input: arr = [5, 2, 4, 3, 1] Output: [1, 2, 3, 4, 5]

Input: arr = [1, 2, 2, 1, 3, 5, 4] Output: [1, 1, 2, 2, 3, 4, 5]

    function sort(arr){
        console.log(arr);
        let sortedArray=[];
        for(let i=0; i<arr.length;i++){
            let swapped = false;
            for(let j=0;j<arr.length - i;j++){
                if(arr[j] > arr[j + 1]){
                    let temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                    swapped = true; 
                }
            }
            if (!swapped)
                break;
        }            
        return arr ;
    }

    console.log("Sorted array : ", sort([64,34, 91, 78,  22, 11, 90, 89]));

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130. Find duplicate elements in an array

Given an array of n integers. The task is to find all elements that have more than one occurrences. The output should only be one occurrence of a number irrespective of the number of occurrences in the input array.

Examples:

Input: {2, 10, 10, 100, 2, 10, 11, 2, 11, 2} Output: {2, 10, 11}

Input: {5, 40, 1, 40, 100000, 1, 5, 1} Output: {5, 40, 1}

    let inputArray = [2, 10, 10, 100, 2, 10, 11, 2, 11, 2]
    console.log(findDuplicates(inputArray));

    function findDuplicates(arr){
        let dupes = [];
        for(let i=0; i<arr.length; i++){
            for(let j=0; j<arr.length-i; j++){
                if(!dupes.includes(arr[i])){
                    if(arr[i]==arr[j]){
                        dupes.push(arr[i])
                        break;
                    }
                }
            }
        }
        return dupes;
    }

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131. Find distinct values from array.

Example:

Input: {2, 10, 10, 100, 2, 10, 11, 2, 11, 2} Output: [ 10, 100, 2, 11 ]

    let inputArray = [2, 10, 10, 100, 2, 10, 11, 2, 11, 2]
    console.log(findDistinct(inputArray));

    function findDistinct(arr){
        let dupes = [];
        let temp = arr[0]
        for(let i=1; i<arr.length;i++){
            if(!dupes.includes(arr[i])){
                dupes.push(arr[i])
            }
        }
        return dupes;
    }

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132. Count number of occurrences (or frequency) in a sorted array

Given a sorted array arr[] and an integer target, the task is to find the number of occurrences of target in given array.

Examples:

Input: arr[] = [1, 1, 2, 2, 2, 2, 3], target = 2 Output: 4 Explanation: 2 occurs 4 times in the given array.

Input: arr[] = [1, 1, 2, 2, 2, 2, 3], target = 4 Output: 0 Explanation: 4 is not present in the given array.

    const arr = [1, 2, 2, 2, 2, 3, 4, 7, 8, 8];
    const target = 2;
    console.log(countFrequency(arr, target));

    function countFrequency(arr, target) {
        let count = 0;
        for (let i = 0; i < arr.length; i++) {
            if (arr[i] === target)
                count++;
        }
        return count;
    }

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133. Dutch National Flag Problem

Sort an array of 0s, 1s and 2s

Given an array arr[] consisting of only 0s, 1s, and 2s. The task is to sort the array, i.e., put all 0s first, then all 1s and all 2s in last.

This problem is the same as the famous “Dutch National Flag problem”. The problem was proposed by Edsger Dijkstra. The problem is as follows:

Given n balls of colour red, white or blue arranged in a line in random order. You have to arrange all the balls such that the balls with the same colours are adjacent with the order of the balls, with the order of the colours being red, white and blue (i.e., all red coloured balls come first then the white coloured balls and then the blue coloured balls).

Examples:

Input: arr[] = {0, 1, 2, 0, 1, 2} Output: {0, 0, 1, 1, 2, 2} Explanation: {0, 0, 1, 1, 2, 2} has all 0s first, then all 1s and all 2s in last.

Input: arr[] = {0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1} Output: {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2} Explanation: {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2} has all 0s first, then all 1s and all 2s in last.

   console.log(xyz)

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134. Balanced Brackets

Check if all brackets are balanced.

Example:

([{}]) should return true (((}}}{][] should return false

const testBrackets = "([{([])}[]{}])";
if (areBracketsBalanced(testBrackets)) {
  console.log("The brackets are balanced in ", testBrackets);
} else {
  console.log("The brackets are not balanced in ", testBrackets);
}

function areBracketsBalanced(str){
    let openingBrackets = ['(', '{', '[']
    let closingBrackets = [')', '}', ']']
    let bracketsMapping = {
        '(' : ')',
        '{' : '}',
        '[' : ']',
    }
    let bracketsStack = []
    for(let i=0; i<str.length; i++){
        if(openingBrackets.includes(str[i])){
            bracketsStack.push(str[i])
        }else{
            let pairOfLastOpenBracket = bracketsMapping[bracketsStack.pop()]
            if(! (pairOfLastOpenBracket == str[i])){
                return false;
            }
        }
    }
    if(! bracketsStack.length == 0){
        return false
    }
    return true;
}

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135. Largest number in Array

Find largest number in a given array

    input = [3,5,8,77,35,98,2,35];

    // Method 1
    function largest(arr){
        let largest = arr[0];
        for(let i=0; i<arr.length; i++){
        if(arr[i]>largest)  { largest=arr[i]}
        }
        return largest
    }
    console.log('Using for loop ', largest(input));


    //Method2 
    function largestNumber(arr){
        return Math.max(...arr)
    }
    console.log('Using Math ', largestNumber(input));

    //Method3
    function largestNumberUsingSort(arr){
        arr.sort((a,b)=> b-a);
        return arr[0];
    }
    console.log('Using sort : ', largestNumberUsingSort(input));

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136. Count vowels in a string

Write a program to count number of vowels in given string

    input = 'uzbekistan';

    // Method 1
    function countVowels(str){
        let vowelsStr = 'aeiouAEIOU';
        let count = 0;
        for(let char of str){
            if(vowelsStr.includes(char)){
            count++;
            }
        }
        return count;
    }
    console.log('Using for loop ', countVowels(input));


    //Method2 
    function countVowelsUsingRegex(str){
        const matches = str.match(/[aeiouAEIOU]/g);
        return matches? matches.length: 0;
        
    }
    console.log('Using regex ', countVowelsUsingRegex(input));

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137. Nested Array

Write a program to flatten a nested array. [[2,3],[2,6,7,9],87,12,[23,[56,22,[45,66,78]]]]

Using Array.flat():

   const nestedArray = [[2,3],[2,6,7,9],87,12,[23,[56,22,[45,66,78]]]];
   var result = nestedArray.flat(Infinity);
   console.log(result);

Using for loop:

   const nestedArray = [[2,3],[2,6,7,9],87,12,[23,[56,22,[45,66,78]]]];
   result = flattenTheArray(nestedArray);
   console.log(result);

    function flattenTheArray(arr){
        let flatArray = [];
        for(let i=0;i<arr.length;i++){
            if(Array.isArray(arr[i])){
                flatArray = flatArray.concat(flattenTheArray(arr[i]))
            }else{
                flatArray.push(arr[i]);
            }
        }
        return flatArray;
    }

Using reduce method:

   result = flattenTheArrayUsingReduce(nestedArray);
   console.log(result);

   function flattenTheArrayUsingReduce(arr){
        return arr.reduce((acc, item)=>{
            return acc.concat(Array.isArray(item)? flattenTheArrayUsingReduce(item):item)
        }, []); 
    }

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138. Reverse a String

Write a program to reverse a string

const input = "uzbekistan";

//Method1 
var result = input.split('').reverse().flat().join('');
console.log("Using short method : ", result);


//Method2
function reverseTheString(str){
    let reversedStr='';
    for(let i=str.length-1;i>=0;i--){
        reversedStr+=str[i];
    }
    return reversedStr
}
result=(reverseTheString(input));
console.log('Using for loop : ', result)

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139. Chain Calculator

Write a program to make a chain calculator in javascript

class ChainCalculator {
    constructor(value = 0) {
      this.value = value;
    }
  
    add(num) {
      this.value += num;
      return this; // Enable chaining
    }
  
    subtract(num) {
      this.value -= num;
      return this;
    }
  
    multiply(num) {
      this.value *= num;
      return this;
    }
  
    divide(num) {
      if (num === 0) {
        throw new Error("Cannot divide by zero");
      }
      this.value /= num;
      return this;
    }
  
    reset() {
      this.value = 0;
      return this;
    }
  
    getResult() {
      return this.value;
    }
  }
  
  
  const calculator = new ChainCalculator();
  const result = calculator
    .add(20)         
    .subtract(5)     
    .multiply(10)     
    .divide(4)      
    .getResult();    
  
  console.log("Result :  ",  result); 

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140. Remove Duplicates from an Array

Write a program to remove duplicates from an array [1,4,5,6,98,56,76,22,98,5]

    const input = [1,4,5,6,98,56,76,22,98,5];


    //Method1 
    var uniqueArray = [...new Set(input)];
    console.log("Using Set : ", uniqueArray);


    //Method2
    function removeDuplicates(arr){
        let result=[];
        arr.forEach(item => {
            if(!result.includes(item)){
                result.push(item)
            }
        })
        return result
    }
    uniqueArray=removeDuplicates(input);
    console.log('Using for each : ', uniqueArray)

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141. Check if Prime number

Write a program to check if given number is prime or not.

    const input = 29;

    function isPrime(num){
        if(num<1) return false;
        if(num===2)  return true;
        for(let i =2 ; i<Math.sqrt(num);i++){
            if(num%i === 0) return false;
        }
        return true;
    }

    result=isPrime(input);
    console.log('Is prime ?  ', result)

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142. Fibonacci Series

Write a program to generate a fibonacci series for n numbers given. Take input = 15. Generate a sequence of 15count. Result should be Result shoud be [0,1,1,2,3,5,8,13,21,34,55,89,144,233,377]

    input = 15;

    function fibonacciSeries(num){
        console.log(num)
        let series = [0,1];
        for(let i=0; i<num-2; i++){
            series.push(series[i]+ series[i+1]);
        }
        return series;
    }

    console.log('Series upto is', fibonacciSeries(input));

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143. Calculate the angle between hour hand and minute hand

Logic

1. Understand the motion of hands:

• The hour hand moves 360degree in 12 hours, so it moves:

360degree/12hours = 30degree/hour

and

30degree/60minutes = 0.5degree/minute

• The minute hand moves 360degree in 60minutes, so it moves:

360degree/60minutes = 6degree/minute

2. Calculate positions of both hands:

• For the hour hand, its position in degrees from 12 o'clock is: Hour hand angle=(Hours×30)+(Minutes×0.5).

• For the minute hand, its position in degrees from 12 o'clock is: Minute hand angle=Minutes×6.

3. Find the difference:

• The absolute difference between the two angles gives the angle between the hands: Angle=∣Hour hand angle−Minute hand angle∣.

4. Account for the smaller angle:

The clock forms a full circle (360degree). If the calculated angle is more than 180 degree, subtract it from 360degree to get the smaller angle.

    console.log(calculateAngle(01,10));

    function calculateAngle(h,m){
        console.log('Input( hh:mm ) ', h, ":", m)
        if(h <0 || m <0 || h >24 || m >60){
            return 'Wrong input'
        }
        if(h == 12){ h = 0; }
        if(h > 12){ h = h-12; }
        if(m == 60){
            m = 0;
            h = h+1;
        }
        
        const perMinMove_minHand = 360/60;
        const perMinMove_hourHand = (360/12)/60;
        const perHourMove_hourHand = 360/12;
        
        angleOfHourHand = (m * perMinMove_hourHand) +  (h*perHourMove_hourHand);
        angleOfMinHand = m*perMinMove_minHand ;
        angleBetweenHands = angleOfHourHand - angleOfMinHand;
        angleBetweenHands = modulus(angleBetweenHands)
        angleBetweenHands = _360degreeFormat(angleBetweenHands);
        
        console.log("Angle between both hands : " , angleBetweenHands)
        
        return angleBetweenHands;
    }

    function modulus(x){
        if(x<1) x=x*-1;
        return x;
    }

    function _360degreeFormat(x){
        if (x>360) x=360-x;
        return x;
    }

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144. Sieve of Eratosthenes

Given a number n, print all primes smaller than or equal to n. It is also given that n is a small number.

    // Sieve of Eratosthenes
    console.log(printAllPrimes(100))

    function printAllPrimes(num){
        let primes = [1,2,3];
        for(let i=4; i<=num; i++){
            let isPrime = checkIfPrime(i);
            if(isPrime) {
                primes.push(i)
            }
        }
        return primes;
    }

    function checkIfPrime(num){
        for(let i=2; i<num; i++){
            if(num%i==0){
                return false;
            }
        }
        return true;
    }

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145. Rearrange an array such that arr[i] = i

Given an array of elements of length n, ranging from 0 to n – 1. All elements may not be present in the array. If the element is not present then there will be -1 present in the array. Rearrange the array such that arr[i] = i and if i is not present, display -1 at that place.

    console.log(rearrange([-1, -1, 6, 1, 9, 3, 2, -1, 4, -1]))

    function rearrange(arr){
        let temp= [];
        for(let i=0; i<arr.length; i++){
            temp[i]=-1;                         //Put -1 in all places by default
        }
        for(let i=0; i<arr.length; i++){
            if(arr[i]!==-1){                    //If arr[i]=i, put it in that place
                temp[arr[i]]=arr[i]
            }
        }
        return temp;
    }

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146. Find sum(1)(2)(3)(4)(5).............()

    let sum = function(a){
        return function(b){
            if(b){
                return sum(a+b)
            }else{
                return a
            }
        }
    }

    // let sum = a => b => return b? sum(a+b) : a;                  // ES6 version for above code.

    let result = sum(1)(2)(3)(4)(5);
    console.log(result())

    let result2 = sum(1)(2)(3)(4)(5)(6)(7)(8)(9);
    console.log(result2())

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147. Convert a nested object to flat object

     let user = {
        name: "Shreyasee",
        address:{
            personal:{
                city: "Pune",
                area: "Hinjewadi"
            },
            office:{
                city: "Pune",
                area: "Kharadi"
            }
        }
    }

    let finalObject = {};

    let magic = (obj, parent) => {
        for(let key in obj){
            if(typeof obj[key] == 'object'){
                magic(obj[key], (parent+'_'+key))
            }else{
                finalObject[parent+'_'+key]= obj[key]
            }
        }
        return finalObject;
    }


    let result = magic(user, "user")
    console.log(result)

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148. Reverse each word without reversing the sentence

    function reverseWords(str) {
    return str
        .split(" ") // Split the string into words
        .map(word => word.split("").reverse().join("")) // Reverse each word
        .join(" "); // Join the words back into a string
    }

    const input = "Hello there, I'm doing good in JS";
    const output = reverseWords(input);
    console.log(output); // Output: "olleH ,ereht m'I gniod doog ni SJ"

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149. xyz

xyz

    console.log(print)

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150. xyz

xyz

    console.log(print)

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151. xyz

xyz

    console.log(print)

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LEETCODE QUESTIONS

---

201. Merge Sorted Array

xyz

    console.log(print)

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202. xyz

xyz

    console.log(print)

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203. xyz

xyz

    console.log(print)

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301. MORE QUESTIONS :

302. Array Questions

• What is an array? How is it different from a linked list?
• How do you find the largest/smallest element in an array?
• How do you reverse an array?
• Explain the difference between a one-dimensional and a multi-dimensional array.
• Write a program to remove duplicates from an array.
• How do you search for an element in an unsorted array? Explain the time complexity.
• How do you find the missing number in an array of integers from 1 to n?

2. String Questions

• What is the difference between mutable and immutable strings in programming?
• How do you check if two strings are anagrams of each other?
• How do you reverse a string?
• Write a program to count the number of vowels in a given string.
• How do you check if a string is a palindrome?

3. Linked List Questions

• What is a linked list? How is it different from an array?
• What are the types of linked lists?
• How do you find the middle element of a singly linked list?
• How do you detect a cycle in a linked list?
• How do you reverse a linked list?
• How do you merge two sorted linked lists into one sorted list?
• Explain the difference between singly linked lists and doubly linked lists.

4. Stack Questions

• What is a stack? Explain its LIFO (Last In, First Out) property.
• How do you implement a stack using arrays or linked lists?
• What are the applications of a stack?
• Write a program to check for balanced parentheses in an expression.
• How do you implement a stack using two queues?

5. Queue Questions

• What is a queue? Explain its FIFO (First In, First Out) property.
• What are the types of queues (e.g., simple queue, circular queue, priority queue)?
• How do you implement a queue using arrays or linked lists?
• What is a circular queue? How is it different from a normal queue?
• How do you implement a queue using two stacks?

6. Tree Questions

• What is a binary tree? How is it different from a binary search tree (BST)?
• What are the types of binary trees (e.g., full, complete, balanced)?
• How do you perform an in-order, pre-order, and post-order traversal of a tree?
• How do you find the height of a binary tree?
• What is a balanced binary tree? How is it maintained?
• How do you check if a binary tree is a BST?

7. Graph Questions

• What is a graph? How is it different from a tree?
• What are the types of graphs (e.g., directed, undirected, weighted)?
• How do you represent a graph (e.g., adjacency matrix, adjacency list)?
• What is the difference between BFS (Breadth-First Search) and DFS (Depth-First Search)?
• How do you detect a cycle in a graph?

8. Hashing Questions

• What is a hash table? How does it work?
• What are collisions in hashing? How do you handle them (e.g., chaining, open addressing)?
• What are the differences between a hash table and a hash map?
• Write a program to find the first non-repeating character in a string using hashing.
• How do you implement a hash table?

9. Sorting and Searching Questions

• What are some common sorting algorithms (e.g., Bubble Sort, Quick Sort, Merge Sort)?
• What is the time complexity of different sorting algorithms?
• How does binary search work? What are its prerequisites?
• What is the difference between linear search and binary search?
• How do you sort an array of integers in ascending/descending order?

10. Miscellaneous Questions

• What is the difference between a stack and a queue?
• What is the difference between linear and non-linear data structures?
• How does a priority queue work?
• What are the advantages of using a linked list over an array?
• What are the applications of different data structures (e.g., stack, queue, tree, graph)?
• How do you measure the efficiency of an algorithm (time complexity and space complexity)?
• What is a dynamic data structure, and how is it different from a static one?

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