leetcode 104 Maximum Depth of Binary Tree(DFS)

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.

/**
 * 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 dfs(TreeNode *r){
        if(r==NULL){
            return 0;
        }    
        return max(dfs(r->left),dfs(r->right)) + 1;
    }
    
    int maxDepth(TreeNode* root) {
        return dfs(root);
    }
};