Save intermediate result into stack and save the stack into result array once its sum == required sum.

```
public class Solution {
private List<List<Integer>> resultList = new ArrayList<List<Integer>>();
public void pathSumInner(TreeNode root, int sum, Stack<Integer>path) {
path.push(root.val);
if(root.left == null && root.right == null)
if(sum == root.val) resultList.add(new ArrayList<Integer>(path));
if(root.left!=null) pathSumInner(root.left, sum-root.val, path);
if(root.right!=null)pathSumInner(root.right, sum-root.val, path);
path.pop();
}
public List<List<Integer>> pathSum(TreeNode root, int sum) {
if(root==null) return resultList;
Stack<Integer> path = new Stack<Integer>();
pathSumInner(root, sum, path);
return resultList;
}
}
```