/**

* 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) {

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

if (root == null)

return result;

Stack<Integer> path = new Stack<Integer>();

preOrder(root, path, result, 0, sum);

return result;

}

private final void preOrder(TreeNode node, Stack<Integer> path, List<List<Integer>> result, int currSum, int expectedSum) {

path.push(node.val);

currSum += node.val;

if (node.left == null && node.right == null && currSum == expectedSum) {

if (currSum == expectedSum) {

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

for (int val : path) {

pathList.add(val);

}

result.add(pathList);

}

}

if (node.left != null) {

preOrder(node.left, path, result, currSum, expectedSum);

}

if (node.right != null) {

preOrder(node.right, path, result, currSum, expectedSum);

}

path.pop();

}

}