Leetcode 113 Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \    / \
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]

Solution 1: DFS

 public class Solution {  
   public List<List<Integer>> pathSum(TreeNode root, int sum) {  
     List<Integer> one=new ArrayList<>();  
     List<List<Integer>> res=new ArrayList<>();  
     dfs(root,0,sum,one,res);  
     return res;  
   }  
   private void dfs(TreeNode x, int k, int sum, List<Integer> one, List<List<Integer>> res) {  
     if (x==null) return;  
     one.add(x.val);  
     k+=x.val;  
     if (x.left==null && x.right==null && k==sum) res.add(new ArrayList<Integer>(one));  
     dfs(x.left,k,sum,one,res);  
     dfs(x.right,k,sum,one,res);  
     one.remove(one.size()-1);  
   }  
 }