/**

 * 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 minDepth(TreeNode* root) {

        if (root == NULL) return ;

        int l = minDepth(root->left);

        int r = minDepth(root->right);

        if (l == ) return r+; //******r+1

        if (r == ) return l+;

        return min(l,r)+;

    }

};