2. Add Two Numbers (Medium)

https://leetcode.com/problems/add-two-numbers/

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

Solutions

class Solution {

    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode ans = null;
        ListNode ptr = null;

        int carry = 0;
        while (l1 != null || l2 != null) {
            int x1 = 0;
            int x2 = 0;

            if (l1 != null) {
                x1 = l1.val;
                l1 = l1.next;
            }

            if (l2 != null) {
                x2 = l2.val;
                l2 = l2.next;
            }

            int sum = (x1 + x2 + carry);
            ListNode x = new ListNode(sum % 10);
            if (ans == null) {
                ans = x;
                ptr = ans;
            } else {
                ptr.next = x;
                ptr = ptr.next;
            }
            carry = sum / 10;
        }

        // Don't forget to take account of the last carry which may not be 0
        if (carry != 0) {
            ptr.next = new ListNode(1);
        }

        return ans;
    }
}

Incorrect Solutions

References