104. Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

return its depth = 3.

1 //Time: O(n), Space: O(logn) recusive stack的空间
2 public int maxDepth(TreeNode root) {
3         if (root == null) {
4             return 0;
5         }
6         
7         return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
8     }