LeetCode/3. Add Two Numbers

Preface

I’ve solved this problem a year ago with a weird way. Today I’ve reviewed this problem.

Link

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

Summary

Reviewing this problem took more than an hour, which made me disappointed and surprise me.
I was very confused assigning outputTail. Same as

{
    l1 = l1.next;
    l2 = l2.next;
    outputTail = outputTail.next;
}

By assigning nextNode to the currentNode which will make loop end at some point. Also we assign node value before going to the next. outputTail.next = node.
Simply I have to remember that to iterate linkedList, assign nextNode to the currentNode in each loop. Then next turn, nextNode will be a currentNode and so on.

Best Solution

        // Best solution
        public ListNode BestSolution(ListNode l1, ListNode l2)
        {
            ListNode output = new ListNode(0);
            ListNode outputTail = output;
            int carry = 0;

            while (l1 != null || l2 != null || carry > 0)
            {
                int val1 = l1 != null ? l1.val : 0;
                int val2 = l2 != null ? l2.val : 0;
                int total = (val1 + val2 + carry) % 10;
                carry = (val1 + val2 + carry) / 10;

                outputTail.next = new ListNode(total);
                outputTail = outputTail.next;

                l1 = l1 != null && l1.next != null ? l1.next : null;
                l2 = l2 != null && l2.next != null ? l2.next : null;
            }

            return output.next;
        }