Question	Details
LC169 – Majority Element	Boyer–Moore Majority Vote Algorithm → Maintain count and number. If the current number is the same, increment count. If different, decrement count. If count becomes 0, update number to the current element.
LC229 – Majority Element II	At most 2 elements can be in the answer. Use a map to count all numbers. If count > threshold (length / 3), add it to the result array and return the array.
LC283 – Move Zeroes	Use left and right pointers. Iterate using right. If nums[right] != 0, swap left and right, then increment left.
LC287 – Find the Duplicate Number	Get index ind. For each iteration, update nums[ind] = -nums[ind]. If nums[ind] < 0, return ind.
LC189 – Rotate Array	Use extra array logic: rotated[(i + k) % len] = nums[i];
LC414 – Third Maximum Number	Sort the array. If the count of unique elements is 3, return nums[i-1]; otherwise, return nums[n-1].
LC55 – Jump Game	Start from the second last index. Check if i + nums[i] >= goal. If yes, update goal = i. Finally, return goal == 0.
LC46 – Permutations	Use DFS (backtracking) with a used set to track visited elements.
LC4 – Median of Two Sorted Arrays	Take a new array, add both arrays to it, sort it, and return the middle element or (mid + mid+1) / 2.
LC33 – Search in Rotated Sorted Array	Apply binary search with conditions based on sorted halves.
LC74 – Search a 2D Matrix	Treat the matrix as a 1D array. Use i = 0, j = length - 1. If matrix[i][j] < target, increment i; else decrement j.
LC153 – Find Minimum in Rotated Sorted Array	Use binary search to find the pivot (minimum element).
LC704 – Binary Search	Divide and conquer approach. If not found, update high = mid - 1 or low = mid + 1.
LC875 – Koko Eating Bananas	Apply binary search on eating speed.
LC121 – Best Time to Buy and Sell Stock I	Track minimum price and calculate max profit using Math.max(maxProfit, prices[i] - minPrice).
LC122 – Best Time to Buy and Sell Stock II	Sum all positive differences. If prices[i] > prices[i-1], then profit += prices[i] - prices[i-1].
LC1 – Two Sum	Use a hashmap to store seen numbers and their indices.
LC13 – Roman to Integer	Add all Roman numeral values using a map and subtract when a smaller value precedes a larger value.
LC49 – Group Anagrams	Use sorted string as the key in a map and return the map values.
LC128 – Longest Consecutive Sequence	Start counting only from sequence heads.
LC187 – Repeated DNA Sequences	Use sliding window + set to track repeated sequences.
LC217 – Contains Duplicate	Use a set. If set.contains(i) return true; else false.
LC347 – Top K Frequent Elements	Use a heap or bucket sort with a priority queue.
LC21 – Merge Two Sorted Lists	Iteratively merge by comparing list1.val and list2.val.
LC143 – Reorder List	Split list using fast/slow pointers, reverse the second half, then merge first list with reversed second list.
LC206 – Reverse Linked List	java\nIterative pointer reversal:\nwhile (head != null) {\n ListNode temp = head.next;\n head.next = node;\n node = head;\n head = temp;\n}\nreturn node;\n
LC19 – Remove Nth Node From End of List	Use two pointers. Move fast pointer n times, then move both slow and fast. When fast becomes null, remove the node pointed by slow.
LC138 – Copy List With Random Pointer	Use hashmap or node-copying technique to clone nodes and random pointers.
LC981 – Time Based Key-Value Store	Store key with list of (timestamp, value) pairs and use binary search on timestamps.
LC7 – Reverse Integer	Reverse digits while handling overflow cases.
LC739 – Daily Temperatures	Use a decreasing stack. Store indices and pop while temperatures[stack.peek()] < temperatures[i].
LC8 – String to Integer (atoi)	Trim spaces, handle sign, and manage overflow.
LC238 – Product of Array Except Self	Use prefix and suffix product arrays.
LC6 – Zigzag Conversion	Simulate zigzag row traversal.
LC3 – Longest Substring Without Repeating Characters	Expand sliding window and shrink when repetition occurs.
LC424 – Longest Repeating Character Replacement	Sliding window approach while tracking max frequency.
LC567 – Permutation in String	Use frequency count and sliding window.
LC76 – Minimum Window Substring	java\nint[] arr = new int[128];\nRead all chars from t into arr.\nIterate s:\nif (arr[s[end++]]-- > 0) count--;\nwhile (count == 0) {\n if (end - start < minLen) update minLen;\n}\n
LC1423 – Maximum Points You Can Obtain From Cards	Use sliding window on total sum and subtract minimum subarray.
LC1461 – Check If String Contains All Binary Codes of Size K	Use a set and add s.substring(i, i + k). If set.size() == 2^k, return true.
LC1876 – Substrings of Size Three With Distinct Characters	Use left and right pointers with a map. If window size is 3 and map size is 3, increment count.
LC2461 – Maximum Sum of Distinct Subarrays With Length K	Sliding window using set and sum tracking.
LC20 – Valid Parentheses	Use stack to match brackets.
LC150 – Evaluate Reverse Polish Notation	Use stack to store operands.
LC155 – Min Stack	Use auxiliary stack or store (value, min) pairs.
LC853 – Car Fleet	Sort cars by position and process using stack logic.
LC14 – Longest Common Prefix	Compare characters across all strings.
LC12 – Integer to Roman	java\nint[] values = {1000,900,500,400,100,90,50,40,10,9,5,4,1};\nString[] symbols = {\"M\",\"CM\",\"D\",\"CD\",\"C\",\"XC\",\"L\",\"XL\",\"X\",\"IX\",\"V\",\"IV\",\"I\"};\nUse StringBuilder and subtract values while num >= values[i].\n
LC226 – Invert Binary Tree	Swap left and right nodes and recursively call invertTree(root.right) and invertTree(root.left).
LC104 – Maximum Depth of Binary Tree	Return 1 + Math.max(maxDepth(root.left), maxDepth(root.right)).
LC11 – Container With Most Water	Use left and right pointers. Move the pointer with the smaller height and calculate max area.
LC42 – Trapping Rain Water	Maintain leftMax and rightMax.
LC141 – Linked List Cycle	Floyd’s cycle detection algorithm (slow and fast pointers).
LC26 – Remove Duplicates From Sorted Array	If nums[i] != nums[j], assign nums[i+1] = nums[j] and increment i.
LC80 – Remove Duplicates From Sorted Array II	Initialize i = j = 2. If nums[i] != nums[j-2], assign nums[j] = nums[i] and increment j.
LC16 – 3Sum Closest	Sort array. Fix one index and use two pointers. Update closest sum using absolute difference comparison.
LC5 – Longest Palindromic Substring	Expand around center technique.