```
class Solution {
public:
int minDepth(TreeNode* root) {
if(!root) return 0;
if(!root->left) return (minDepth(root->right) + 1);
if(!root->right) return (minDepth(root->left) + 1);
return (min(minDepth(root->left),minDepth(root->right)) + 1);
}
};
```