Greatest Common Divisor Euclidean algorithm public int gcd(int a, int b) { while (b != 0) { int tmp = b; b = a % b; a = tmp; } return a; } Variants Greatest...

Subtree of Another Tree Binary Lifting This is a good tutorial on Binary Lifting. Kth Ancestor of a Tree Node // dp[i][j] = j-th node's (2 ^ i)-th ancestor in the path private int[][] dp; priva...

Selection algorithm Heap Sort Kth Largest Element in an Array public int findKthLargest(int[] nums, int k) { // min heap Queue<Integer> pq = new PriorityQueue<>(); for (i...

Traversal Preorder Binary Tree Preorder Traveral Recursion public List<Integer> preorderTraversal(TreeNode root) { List<Integer> list = new ArrayList<>(); helper(root, li...

Fundamentals The most commonly way of DFS is to call a helper function recursively. Due to the nature of recursion, we can instead use a Stack. Keys and Rooms Recursion public boolean canVisitA...

Sort an Array Quicksort Quicksort: not stable Lomuto Partition Scheme public int[] sortArray(int[] nums) { quickSort(nums, 0, nums.length - 1); return nums; } private void quickSor...

Iteration while iterating through an array, keep a running state to some variables. Maximum Value of an Ordered Triplet II long long maximumTripletValue(vector<int>& nums) { long l...

Definition a[i_0], a[i_1], ..., a[i_k] Where 0 <= i_0 < i_1 < ... < i_k <= a.length Algorithm Greedy Shortest Impossible Sequence of Rolls public int shortestSequence(int[] roll...

Definition a[i], a[i + 1], ..., a[j] Where 0 <= i <= j <= a.length Algorithm Minimum Moves to Make Array Complementary public int minMoves(int[] nums, int limit) { // delta array ...

Distant Barcodes Let n = barcodes.length. Find the elements barcodes[i] with the most occurrences \(o_{max}\). Assume an element barcodes[k] has occurences \(o_k\). Steps: Put barcodes[i] to t...