Tree Based Problem

Treat “Tree Based Problem” as an incomplete prompt, not as permission to guess. Ask whether the interviewer wants a binary-tree operation, an n-ary traversal, a BST rule, or a tree-graph algorithm, and request examples plus constraints. Then select the smallest fitting pattern. Postorder DFS is best when a node depends on both child summaries; preorder is useful for carrying a root-to-node state; BFS is best for levels or minimum edges in an unweighted tree. Name the invariant before implementation, for example, “queue contains exactly the next frontier” or “dfs returns the answer for this subtree.” Any complete traversal touches each node once, O(n) time, using O(h) DFS stack or O(w) BFS space. Verify null roots, leaves, skew, duplicate values, and recursion limits.