LeetCode 257. 二叉树的所有路径（DFS）

示例:

输入:

   1
 /   \
2     3
 \
  5

输出: ["1->2->5", "1->3"]

解释: 所有根节点到叶子节点的路径为: 1->2->5, 1->3

class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        string path;
        vector<string> ans;
        walk(root, path, ans);
        return ans;
    }
    void walk(TreeNode* root, string path, vector<string>& ans) 
    {
    	if(root == NULL)
    		return;
    	walk(root->left, path+to_string(root->val)+"->", ans);
    	walk(root->right, path+to_string(root->val)+"->", ans);
    	if(!root->left && !root->right)
        {
            path += to_string(root->val);
            ans.push_back(path);   
        }
    }
};