#include "stdbool.h"
#define NULL ((void *)0)

//Definition for a binary tree node.
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

//深度优先
int maxDepth(struct TreeNode* root){
    if(root == NULL)
        return 0;
    else
        return fmax(maxDepth(root->left), maxDepth(root->right))+1;
}