LeetCode/21. MergeTwoSortedLists

https://leetcode.com/problems/merge-two-sorted-lists/

Summary

This was asking same question as AddTwoNumbers. Can properly reference next in LinkedArray.
Still quite slow, but solving much faster than before.

Solutions

My Solution

I was a bit confused which order comes first outputTail.next or outputTail. But it is obvious.
The proper steps will be,

  1. Assign a new value to the outputTail.next via new ListNode(x).
  2. Change the pointer(ref) of outputTail to outputTail.next which is a new value has been assigned.
public ListNode MergeTwoLists(ListNode l1, ListNode l2)
{
    var output = new ListNode(0);
    var outputTail = output;

    while (l1 != null || l2 != null)
    {
        if (l1 == null)
        {
            outputTail.next = l2;
            break;
        }

        if (l2 == null)
        {
            outputTail.next = l1;
            break;
        }

        if (l1.val <= l2.val)
        {
            outputTail.next = new ListNode(l1.val);
            outputTail = outputTail.next;
            l1 = l1.next;
        }
        else
        {
            outputTail.next = new ListNode(l2.val);
            outputTail = outputTail.next;
            l2 = l2.next;
        }
    }

    return output.next;
}

Best Solution

I should make it simpler like the code below. Also I don’t need to assign a New ListNode just change the ref of the pointer.

public ListNode MergeTwoLists(ListNode l1, ListNode l2)
{
    var output = new ListNode(0);
    var outputTail = output;

    while (l1 != null && l2 != null)
    {
        if (l1.val <= l2.val)
        {
            outputTail.next = l1;
            l1 = l1.next;
        }
        else
        {
            outputTail.next = l2;
            l2 = l2.next;
        }
        outputTail = outputTail.next;
    }

    outputTail.next = l1 != null ? l1 : l2;

    return output.next;
}
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