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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.

分析

题意是：给定一颗二叉树，求出它的最大深度

对树的问题，递归总是一种思路。对于这个求二叉树深度的问题，我们可以归结出这样一种思路，从根节点开始 求出它的左子树深度leftDepth和右子树深度rightDepth，求出leftDepth和rightDepth的最大值，那么再加一就是根 点的最大深度；递归的执行下去，结束条件就是当节点是叶子节点是，返回深度1。

Code

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 class Solution {
 public:
    int maxDepth(TreeNode *root) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if( !root )
            return 0;
        int leftDepth = 0, rightDepth = 0;
        if( root->left )
            leftDepth = maxDepth(root->left);
        if( root->right )
            rightDepth = maxDepth(root->right);
        return 1 + std::max(leftDepth, rightDepth);
    }
};

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