[LeetCode] 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"]

输出一个树的路径。使用递归的方法

/**
 * 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 == nullptr)
            return res;
        binaryTreePathsCore(res, root, to_string(root->val));
        return res;
    }
    
    void binaryTreePathsCore(vector<string>& res, TreeNode* root, string s) {
        if (root->left == nullptr && root->right == nullptr) {
            res.push_back(s);
            return;
        }
        if (root->left != nullptr)
            binaryTreePathsCore(res, root->left, s + "->" + to_string(root->left->val));
        if (root->right != nullptr)
            binaryTreePathsCore(res, root->right, s + "->" + to_string(root->right->val));
    }
};
// 6 ms