Path Sum II

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]
]

Solution:

/**
 * 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>> ans = new ArrayList<>();
        if(root==null) return ans;
        List<Integer> path = new ArrayList<>();
        helper(ans, path, root, sum);
        return ans;
    }
    
    public void helper(List<List<Integer>> list, List<Integer> path, TreeNode root, int sum) {
        if(root.left==null && root.right==null && root.val==sum){
            List<Integer> res = new ArrayList<>(path);
            res.add(sum);
            list.add(res);
        }

        path.add(root.val);
        if(root.left!=null) helper(list, path, root.left, sum-root.val);
        if(root.right!=null) helper(list, path, root.right, sum-root.val);
        path.remove(path.size()-1);

    }
}