104. Maximum Depth of Binary Tree

摘要： 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 farth...

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],

3
/ \
920
/\
157
return its depth = 3.

難度：easy

題目：給定二叉樹，找出最大深度。

最大深度指的是最長路徑從根結點到最遠的葉子結點。

思路：後序遍歷

Runtime: 0 ms, faster than 100.00% of Java online submissions for Maximum Depth of Binary Tree.

Memory Usage: 27.8 MB, less than 73.06% of Java online submissions for Maximum Depth of Binary Tree.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *int val;
 *TreeNode left;
 *TreeNode right;
 *TreeNode(int x) { val = x; }
 * }
 */
class Solution {
public int maxDepth(TreeNode root) {
if (null == root) {
return 0;
}

return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
}
}