二叉树的所有路径

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