二叉樹的深度

題目：Maximum Depth of Binary Tree

題目詳情:

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.

翻譯：

有一個二叉樹，得到它的最大深度

答案：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null)
            return 0;
        else {
            int leftDepth = maxDepth(root.left);
            int rightDepth = maxDepth(root.right);
            return 1 + Math.max(leftDepth, rightDepth);
        }
    }
}