Path Sum II （未搞定）

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]
]

思想：用dfs思想求解

注意事项： 对标记节点，要控制回退

java代码：

1. ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
2. ArrayList<Integer> cur = new ArrayList<Integer>();
3. void pathSumHelper(TreeNode root,int sum) {
4. if(root==null) return; //注意判断
5. cur.add(root.val);
6. if(root.left == null && root.right == null) {
7. if(root.val == sum) {
8. res.add(new ArrayList<Integer>(cur));
9. }
10. cur.remove(cur.size()-1); //注意回退
11. return;
12. }
13. pathSumHelper(root.left,sum-root.val);
15. pathSumHelper(root.right,sum-root.val);
16. cur.remove(cur.size()-1); //注意回退
17. }
18. public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
19. if(root==null) return res;
21. pathSumHelper(root,sum);
22. return res;
23. }