[leetcode]257. Binary Tree Paths二叉树路径

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

题目

给定一棵二叉树，求出所有根到叶的路径。

思路

DFS， Very straightforward

代码

 class Solution {
     public List<String> binaryTreePaths(TreeNode root) {
         List<String> result = new ArrayList<>();
         if(root == null) return result;
         helper(root, result, "");
         return result;
     }

     private  void helper (TreeNode root, List<String> result,  String path){
         // leaf node
         if(root.left ==null && root.right ==null) {
            result.add(path + root.val);
         }
         // dfs
         if(root.left!=null){
             helper(root.left, result, path+root.val+ "->");
         }
         if(root.right!=null){
             helper(root.right, result, path+root.val+"->");
         }
     }
 }