480. 二叉树的所有路径递归

   1
 /   \
2     3
 \
  5

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

 vector<string> binaryTreePaths(TreeNode* root) 
     {
         vector<string> res;
         if(!root)
            return res;
         binaryTreePathsCore(root,res,to_string(root->val));
            return res;
         
     }
     
     
     
    void binaryTreePathsCore(TreeNode *root,vector<string> &vstring,string str)
     {
         if(root->left==NULL&&root->right==NULL)
         {
             vstring.push_back(str);
             return;
         }
         if(root->left)
         {
             binaryTreePathsCore(root->left,vstring,str+"->"+to_string(root->left->val));
         }
          if(root->right)
         {
             binaryTreePathsCore(root->right,vstring,str+"->"+to_string(root->right->val));
         }
         
     }