104. Maximum Depth of Binary Tree

Return the maximum depth of a binary tree: the number of nodes on the longest root-to-leaf path.

Push (node, depth) pairs onto a stack and track the largest depth seen.

1function maxDepth(root: TreeNode | null): number {
2  const stack: [TreeNode | null, number][] = [[root, 1]];
3  let best = 0;
4  while (stack.length) {
5    const [n, d] = stack.pop()!;
6    if (!n) continue;
7    best = Math.max(best, d);
8    stack.push([n.left, d + 1], [n.right, d + 1]);
9  }
10  return best;
11}

best = 0

tree

stack (node:depth)

3:1

Push (root, 1).

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