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Invert Binary Tree — LeetCode 226 Google Whiteboard Classic
LeetCode 226 — Invert Binary Tree, the famous Max Howell / Google whiteboard rejection question. Solve recursively in 4 lines or iteratively with BFS in O(n) time.
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Symmetric Tree — LeetCode 101 Mirror Recursion Pattern
LeetCode 101 — Symmetric Tree, asked at Amazon, Microsoft and Bloomberg. Compare opposite subtrees with a two-pointer recursive helper to check mirror symmetry in O(n) time.
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Path Sum — LeetCode 112 Root-to-Leaf DFS for FAANG Interviews
LeetCode 112 — Path Sum, asked at Amazon, Microsoft, Apple and Meta. Use DFS with a running remainder to detect any root-to-leaf path that sums to a target value in O(n) time.
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Same Tree — LeetCode 100 Parallel DFS Comparison
LeetCode 100 — Same Tree, asked at Amazon, Meta, Google and Apple. Walk both trees simultaneously and return false on the first structural or value mismatch in O(n) time.
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Balanced Binary Tree — LeetCode 110 Postorder Height with Early Exit
LeetCode 110 — Balanced Binary Tree, asked at Amazon, Meta, Google and Microsoft. Use a postorder DFS that returns -1 on imbalance to solve it in O(n) time instead of the naive O(n log n).
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