Binary Tree Paths @LeetCode

PROBLEM :

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"]

--------------------------------------------------------------------------------
SIMPLE c++ IMPLEMENTATION :
--------------------------------------------------------------------------------

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> vec ;
        if(root==NULL)
            return vec ;
           
        string str="" ;
        CheckAllPaths(root,str,vec) ;
        return vec ;
    }
   
    void CheckAllPaths(TreeNode *root,string str,vector<string> &vec){
        if(root==NULL)
            return ;
           
        if(str=="")  
            str+=to_string(root->val) ;
        else{
            str+="->" ;
            str+=to_string(root->val) ;
        }
       
        if(root->left==NULL&&root->right==NULL)
            vec.push_back(str) ;
           
        CheckAllPaths(root->left,str,vec) ;
        CheckAllPaths(root->right,str,vec) ;
    }
};

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