class Solution {
public:
    /**
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    int DFS(TreeNode* node){
        if(node==NULL)
            return 0;
        int depth=1;
        int left=DFS(node->left);
        int right=DFS(node->right);
        return left>right?depth+left:depth+right;
    }
    int maxDepth(TreeNode* root) {
        // write code here
        int depth=DFS(root);
        return depth;
    }
};