minimum depth of binary tree

1 /*Given a binary tree, find its minimum depth.The minimum depth is the number of nodes
2     along the shortest path from the root node down to the nearest leaf node.*/
3     int minDepth(TreeNode *root)
4     {
5         if(root == NULL) return 0;        
6         if (root->left==NULL) return 1 + minDepth(root->right);
7         if (root->right == NULL) return 1 + minDepth(root->left);
8         return 1 + min(minDepth(root->left), minDepth(root->right));        
9     }