树、递归————二叉树的最大深度

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        int maxdepth=0;
        if(root==NULL) return 0;//递归基本情况分析
        else{
            maxdepth = max(maxDepth(root->left),maxDepth(root->right));//递归
            return maxdepth+1;
        }
    }
};