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LeetCode 617 — Merge Two Binary Trees, asked at Amazon, Apple, Meta and Microsoft. Walk both trees in parallel, sum overlapping nodes, and reuse existing pointers in O(n) time.
LeetCode 938 — Range Sum of BST, asked at Amazon, Facebook (Meta), Google and Apple. Use the BST property to prune entire out-of-range subtrees and run in O(h + k) time.
LeetCode 700 — Search in a BST, asked at Amazon, Microsoft, Apple and Meta. Eliminate half the tree at each step using the BST property and finish in O(h) time, O(1) iterative space.
LeetCode 102 — Binary Tree Level Order Traversal, asked at Amazon, Meta, Google and Microsoft. The canonical BFS template that powers Right Side View, Zigzag, Largest in Each Row and 30+ other problems.
LeetCode 103 Binary Tree Zigzag Level Order Traversal — frequently asked at Amazon, Meta, Microsoft, and Bloomberg. Learn the BFS toggle pattern with deque appendleft for O(n) time.