Path Sum II leetcode java

题目：

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]
]

题解： 这道题除了要判断是否有这样的一个path sum，还需要把所有的都可能性结果都返回，所以就用传统的DFS递归解决子问题。代码如下：

1     public void pathSumHelper(TreeNode root, int sum, List <Integer> sumlist, List<List<Integer>> pathlist){
2         if(root==null)
3             return;
4         sumlist.add(root.val);
5         sum = sum-root.val;
6         if(root.left==null && root.right==null){
7             if(sum==0){
8                 pathlist.add(new ArrayList<Integer>(sumlist));
9             }
10         }else{
11             if(root.left!=null)
12                 pathSumHelper(root.left,sum,sumlist,pathlist);
13             if(root.right!=null)
14                 pathSumHelper(root.right,sum,sumlist,pathlist);
15         }
16         sumlist.remove(sumlist.size()-1);
17     }
18
19     public List<List<Integer>> pathSum(TreeNode root, int sum) {
20         List<List<Integer>> pathlist=new ArrayList<List<Integer>>();
21         List<Integer> sumlist = new ArrayList<Integer>();
22         pathSumHelper(root,sum,sumlist,pathlist);
23         return pathlist;
24     }

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