257. Binary Tree Paths

Given a binary tree, return all root-to-leaf paths.

Note: A leaf is a node with no children.

Example:

Input:

   1
 /   \
2     3
 \
  5

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

Explanation: All root-to-leaf paths are: 1->2->5, 1->3

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

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