257. Binary Tree Paths

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"]

LeetCode AC代码：

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