Add Two Numbers

LeetCode Q 2 - 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.

Solution

Take care to boundary cases.

Code:

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
	ListNode dummy = new ListNode(-1), curr = dummy;
	
	int carry = 0;
	
	while (l1 != null || l2 != null) {
		int num = carry; 
		num += (l1 == null ? 0 : l1.val);
		num += (l2 == null ? 0 : l2.val);
		curr.next = new ListNode (num % 10);
		carry = num / 10;
		if (l1 != null) l1 = l1.next;
		if (l2 != null) l2 = l2.next;
		curr = curr.next;
	}
	
	if (carry == 1)
		curr.next = new ListNode (1);
	
	return dummy.next;
}