1582 articles
LC 993 Cousins in Binary Tree checks if two nodes are at the same depth with different parents. The clean O(n) BFS solution processes one level at a time — a foundational tree problem tested at Amazon and Microsoft.
LC 222 Count Complete Tree Nodes has an O(log^2 n) solution that exploits perfect subtree detection — a FAANG interview problem where the naive O(n) answer is wrong. Learn the left/right spine height comparison trick tested at Amazon and Google.
LC 701 Insert into a BST traverses left or right based on value comparisons until finding a null position. The O(h) recursive solution is a BST fundamentals question tested at Amazon and Microsoft — always insert at a leaf.
LC 589 N-ary Tree Preorder and LC 590 Postorder Traversal generalize binary tree DFS to trees with any number of children. These easy problems build the foundation for harder n-ary tree problems asked at Amazon and Google.
LC 427 Construct Quad Tree builds a spatial partitioning tree from a 2D binary grid by recursively splitting non-uniform regions into four quadrants. This divide-and-conquer problem is tested at Amazon and Google and models real-world image compression and spatial indexing.