EasyCoding

Maximum Depth of Binary Tree

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2Answer out loud, not in your head

3Then compare with the answer below

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01Define the depth of an empty subtree as zero.
02Recursively compute left and right subtree depths.
03Return one plus the larger child depth.
04State whether the definition counts nodes or edges and handle an empty tree.

Reference answer

Define depth(node) as the number of nodes on the longest path from node down to a leaf. The base case is depth(null) = 0. For a real node, return 1 + max(depth(node.left), depth(node.right)). This directly mirrors the tree's recursive structure and visits each node once, so time is O(n). Recursive stack space is O(h), where h is the tree height; a skewed tree can therefore use O(n) stack space. An iterative BFS alternative processes the tree level by level and increments a counter after each level. BFS also takes O(n) time but may hold up to the tree's maximum width in memory. Clarify whether depth counts nodes or edges; this problem's conventional answer counts nodes, giving depth one for a single-node tree and zero for an empty tree.

Then expect these follow-ups

How would you compute minimum depth?
Tests: tree edge cases
When would BFS use less memory than DFS here?
Tests: trade-offs

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