2. Add Two Numbers #

Problem Statement: #

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 contains a single digit. Add the two numbers and return the sum as a linked list.

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

Example 1: #

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Example 2: #

Input: l1 = [0], l2 = [0]
Output: [0]

Example 3: #

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

Constraints: #

• The number of nodes in each linked list is in the range [1, 100].
• 0 <= Node.val <= 9
• It is guaranteed that the list represents a number that does not have leading zeros.

Solution: #

public ListNode addTwoNumbers(ListNode a, ListNode b) {
  ListNode dummy = new ListNode(0),
      tail = dummy;
  int carry = 0;
  while (a != null || b != null) {
    int x = (a != null) ? a.val : 0,
        y = (b != null) ? b.val : 0,
        sum = carry + x + y;
    carry = sum / 10;
    tail.next = new ListNode(sum % 10);
    tail = tail.next;
    if (a != null)
      a = a.next;
    if (b != null)
      b = b.next;
  }
  if (carry > 0)
    tail.next = new ListNode(carry);
  return dummy.next;
}

... #