1 class Solution { 2 public: 3     int minDepth(TreeNode *root) { 4         if (root == nullptr) return 0; 5         if (root->left != nullptr&&root->right != nullptr) 6         { 7             int lDepth = minDepth(root->left); 8             int rDepth = minDepth(root->right); 9             return (lDepth<rDepth?lDepth+1:rDepth+1);10         }11         if (root->left != nullptr)12         {13             return 1+minDepth(root->left);14         }15         if (root->right != nullptr)16         {17             return 1+minDepth(root->right);18         }19         return 1;//只有一个根节点时。20     }21 };