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Problem

Maximum Depth of Binary Tree

LeetCode #104Easy

Depth = 1 + max(left, right)

Given the root of a binary tree, return its maximum depth: the number of nodes along the longest path from the root down to the farthest leaf.

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Recursive DFS (post-order)

time O(n)space O(h)

step 1 / 18

binary tree

call stack ↓

(returned)

Recursive DFS (post-order)


▸
1depth(node):
2    push frame
3    if node is null: return 0      // base case
4    L = depth(node.left)
5    R = depth(node.right)
6    return 1 + max(L, R)           // combine

state

goallongest root→leaf

line 1Maximum depth = the longest root-to-leaf chain. DFS expresses this in one line: a node's depth is 1 + the deeper of its two children. We let recursion (and the call stack) do the bookkeeping — watch the values bubble UP from the leaves.