Maximum Depth of Binary Tree

题目：

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.

分析：

divide and conquer，三分钟可以做完，没有bug

解法：

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int maxDepth(TreeNode root) {
        // write your code here
        if (root == null) {
            return 0;
        } 
        int lHeight = maxDepth(root.left);
        int rHeight = maxDepth(root.right);
        return Math.max(lHeight, rHeight) + 1;
    }
}