https://leetcode.com/problems/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

程式碼：

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