257. Binary Tree Paths

Given the root of a binary tree, return all root-to-leaf paths in any order.

A leaf is a node with no children.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    vector<string> res;
    void helper(TreeNode* node, string path) {
        if(!node->left and !node->right) res.push_back(path);
        else {
            if(node->left) helper(node->left, path + "->" + to_string(node->left->val));
            if(node->right) helper(node->right, path + "->" + to_string(node->right->val));
        }
    }
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        if(!root) return {};
        helper(root, to_string(root->val));
        return res;
    }
};