Binary Tree Paths

For example, given the following binary tree:

1 /   \2     3 \  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

1.解题思路

求根节点到叶子节点的路径集合，采用深度搜索，利用递归实现。

2.代码

public class Solution {    List
    
      res=new ArrayList
     
      ();    public List
      
        binaryTreePaths(TreeNode root) {        helper(root,new String());        return res;            }    private void helper(TreeNode root,String pre){        if(root==null)  return;        if(root.left==null&&root.right==null){            res.add(pre+root.val);            return;        }        helper(root.left,pre+root.val+"->");        helper(root.right,pre+root.val+"->");    }}