Root to Leaf Paths With Sum

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]
]

Method:

DFS

Solution:

Time: O(n)
Space: O(n)

/**
 * Definition for binary tree
 * class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) {
 *      val = x;
 *      left=null;
 *      right=null;
 *     }
 * }
 */
public class Solution {
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode A, int B) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        ArrayList<Integer> curr = new ArrayList<>();
        helper(result, curr, A, B);
        return result;
    }
    
    private void helper(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> curr, TreeNode A, int B) {
        if (A == null) return;
        if (A.left == null && A.right == null) {
            if (A.val == B) {
                curr.add(A.val);
                result.add(new ArrayList<>(curr));
                curr.remove(curr.size() - 1);
                return;
            } 
        }
        if (A.left != null) {
            curr.add(A.val);
            helper(result, curr, A.left, B - A.val);
            curr.remove(curr.size() - 1);
        }
        if (A.right != null) {
            curr.add(A.val);
            helper(result, curr, A.right, B - A.val);
            curr.remove(curr.size() - 1);
        }
    }
}