Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers % 1003.

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = (12 + 13) % 1003 = 25 % 1003 = 25.

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 int sumNumbers(TreeNode A) {
        List<Integer> sums = new ArrayList<>();
        getSums(sums, A, 0);
        int sum = 0;
        for (int i : sums) {
            sum += i;
        }
        return sum % 1003;
    }
    
    private void getSums(List<Integer> sums, TreeNode A, int num) {
        if (A == null) return;
        if (A.left == null && A.right == null) {
            sums.add((num * 10) % 1003 + A.val % 1003);
            return;
        }
        if (A.left != null) {
            getSums(sums, A.left, (num * 10) % 1003 + A.val % 1003);
        }
        if (A.right != null) {
            getSums(sums, A.right, (num * 10) % 1003 + A.val % 1003);
        }
    }
}