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.

接口：

class Solution {
public:
    /**
     * @param root: The root of binary tree.
     * @return: An integer
     */
    int maxDepth(TreeNode *root) {
        // write your code here

    }
};

分析：

简单题目能够handle住，所以用个divide-and-conquer，返回int型。

定义结点：

struct TreeNode{
public:
  int val;
  TreeNode* left;
  TreeNode* right;
  TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

解法：

class Solution {
public:
    /**
     * @param root: The root of binary tree.
     * @return: An integer
     */
    int maxDepth(TreeNode *root) {
        // write your code here
        if (root == NULL) {
            return 0;
        }

        int left = maxDepth(root->left) + 1;
        int right = maxDepth(root->right) + 1;

        return max(left, right);
    }
};