257. Binary Tree Paths

 1 class Solution {
 2 public:
 3     vector<string> binaryTreePaths(TreeNode* root) {
 4         vector<string> res;
 5         if (!root) return res;
 6         dfs(res,root,to_string(root->val));
 7         return res;
 8     }
 9         
10     void dfs(vector<string> res, TreeNode* root, string path){
11         if (!root->left && !root->right){
12             res.push_back(path);
13             return;
14         }
15         if (root->left) dfs(res,root->left,path+"->"+to_string(root->left->val));
16         if (root->right) dfs(res, root->right, path+"->"+to_string(root->right->val));
17     }                                                                      
18 };