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]

]

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

public class Solution {

public List<List<Integer>> pathSum(TreeNode root, int sum) {

ArrayList<List<Integer>> lists = new ArrayList<List<Integer>>();

if (root == null) {

return lists;

}

helper(root, new ArrayList<Integer>(), lists, sum);

return lists;

}

public void helper(TreeNode root, List<Integer> list, List<List<Integer>> lists, int sum) {

if (root.left == null && root.right == null) {

ArrayList<Integer> tmp = new ArrayList<Integer>(list);

if (root.val == sum) {

tmp.add(root.val);

lists.add(tmp);

}

return;

}

ArrayList<Integer> tmp = new ArrayList<Integer>(list);

tmp.add(root.val);

sum -= root.val;

if (root.left != null) {

helper(root.left, tmp, lists, sum);

}

if (root.right != null) {

helper(root.right, tmp, lists, sum);

}

}

}