257. Binary Tree Paths

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

 

   1

 /  

2     3

 

  5

 

All root-to-leaf paths are:

["1->2->5", "1->3"]

 

Solution1: dfs, recursion. use the dfs function.

 

class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> res;
        if (!root) return res;
        dfs(res,root,to_string(root->val));
        return res;
    }
        
    void dfs(vector<string> res, TreeNode* root, string path){
        if (!root->left && !root->right){
            res.push_back(path);
            return;
        }
        if (root->left) dfs(res,root->left,path+"->"+to_string(root->left->val));
        if (root->right) dfs(res, root->right, path+"->"+to_string(root->right->val));
    }                                                                      
};