二叉树的所有路径

给一棵二叉树，找出从根节点到叶子节点的所有路径。

您在真实的面试中是否遇到过这个题？ Yes
样例
给出下面这棵二叉树：

   1
 /   \
2     3
 \
  5
所有根到叶子的路径为：

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

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param root the root of the binary tree
     * @return all root-to-leaf paths
     */
    vector<string> binaryTreePaths(TreeNode* root) {
        // Write your code here
        vector<string> results;
        vector<int> temp;
        if(root==NULL) {
            
            return results;
        }
        preTravel(root,temp,results);
        return results;
    }
    
    void preTravel(TreeNode* root,vector<int> &temp,vector<string> &results) {
        
         temp.push_back(root->val);
        if(root->left == NULL&&root->right == NULL) {
             string str;
           for(auto i: temp){
               str += to_string(i) + "->";
           }
           str = str.substr(0,str.size()-2);
           results.push_back(str);
           
        } 
        if (root->left != NULL) {
              preTravel(root->left,temp,results);
        }
         if (root->right != NULL) {
             preTravel(root->right,temp,results);
         }
        
        
        
        temp.pop_back();
    }
};