1582 articles
LeetCode 199 Binary Tree Right Side View — high-frequency at Amazon, Meta, Google, and Apple. Two clean approaches: BFS taking last node per level and DFS visiting right-first.
LeetCode 113 Path Sum II — Medium tree backtracking favorite at Amazon, Meta, Microsoft. Collect every root-to-leaf path summing to target with DFS plus path append-and-pop.
LeetCode 543 Diameter of Binary Tree — top Tree DP problem at Amazon, Meta, Google, Bloomberg. Single DFS that returns height while tracking the longest path through any node.
LeetCode 98 Validate Binary Search Tree — high-frequency at Amazon, Meta, Google, Apple. Pass min and max bounds down through DFS so every node is strictly within its valid range.
LeetCode 230 Kth Smallest Element in a BST — Amazon, Meta, Uber favorite. Iterative inorder with a stack stops at the kth pop in O(h+k) time.