2. Add Two Numbers [Medium]

You are given twonon-emptylinked lists representing two non-negative integers. The digits are stored inreverse orderand 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.

Analyse:

兩個List的Node依序相加, 若結果大於10則記錄需進位.

Solution:

func addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {   
        var node1 = l1;
        var node2 = l2;
        var output = ListNode(0);
        var head = output;

        var carry = 0;

        while(node1 != nil || node2 != nil) {
            var sum = carry;

            if(node1 != nil) {
                sum = sum + node1!.val;
                node1 = node1!.next
            } 

            if(node2 != nil) {
                sum = sum + node2!.val;
                node2 = node2!.next
            }

            let value = sum % 10;
            carry = sum / 10;

            var newNode = ListNode(value);
            output.next = newNode;
            output = output.next!;
        }

        if(carry != 0) {
            var newNode = ListNode(carry);
            output.next = newNode;
            output = output.next!;
        }

        return head.next;

}