class Solution

{

public:

    void dfs(TreeNode *root,int step,int &MAX)

    {

        if(root==NULL)

        {

            if(MAX<step) MAX=step;

            return ;

        }

        dfs(root->left,step+1);

        dfs(root->right,step+1);

    }

    int maxDepth(TreeNode *root)

    {

        int MAX=0;

        dfs(root,step,MAX);

        return MAX;

    }

};


    

      class Solution {

public:

    int maxDepth(TreeNode *root) {

        if(root==NULL) return 0;

        int leftDepth=maxDepth(root->left);

        int rightDepth=maxDepth(root->right);

        return max(leftDepth,rightDepth)+1;

    }

};