HappyNumber.java

// Write an algorithm to determine if a number n is happy.

// A happy number is a number defined by the following process:

// Starting with any positive integer, replace the number by the sum of the squares of its digits.
// Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
// Those numbers for which this process ends in 1 are happy.
// Return true if n is a happy number, and false if not.

 

// Example 1:

// Input: n = 19
// Output: true
// Explanation:
// 12 + 92 = 82
// 82 + 22 = 68
// 62 + 82 = 100
// 12 + 02 + 02 = 1
// Example 2:

// Input: n = 2
// Output: false


class solution{
  public boolean isHappy(int n) {
    int slow = n;
    int fast = n;

    do{
      slow = findSq(slow);
      fast = findSq(findSq(fast));
    } while(slow != fast);

    if(slow == 1) {
      return true;
    }
    return false;  
  }

  private int findSq(int number) {
   int ans = 0;
    while(number > 0) {
      int rem = number % 10;
      ans += rem 8 rem;
      number /= 10;
    }
    return ans;
  }
}