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.

For example,

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 = 25.

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 int sumNumbers(TreeNode root) {

        if(root == null) return 0;
        int[] value = new int[1];
        sumNumbers(root, value, new ArrayList<>());
        return value[0];
    }

    public void sumNumbers(TreeNode root, int[] value, List<Integer> current) {
        ;
        current.add(root.val);
        if (root.left == null && root.right == null) {
            value[0] += convert(current);
        } else {
            if (root.left != null) {
                sumNumbers(root.left, value, current);
            }

            if (root.right != null) {
                sumNumbers(root.right, value, current);
            }
        }
        if (!current.isEmpty())
            current.remove(current.size() - 1);
    }

    public int convert(List<Integer> list) {
        int sum = 0;
        int temp = 1;

        for (int i = list.size() - 1; i >= 0; i--) {
            sum += temp * list.get(i);
            temp *= 10;
        }

        return sum;
    }
}