Issues with Implementing Merge Sort with Linked Lists in C# - Incorrect Output Order
Quick question that's been bugging me - I'm writing unit tests and I'm currently trying to implement the Merge Sort algorithm to sort a singly linked list in C#. However, I'm running into an issue where the output order of the elements is incorrect after sorting. I've followed the typical divide-and-conquer strategy, but I suspect the merging logic might be flawed. Here's the code I've written so far: ```csharp public class ListNode { public int val; public ListNode next; public ListNode(int x) { val = x; } } public class Solution { public ListNode SortList(ListNode head) { if (head == null || head.next == null) return head; ListNode mid = GetMiddle(head); ListNode left = SortList(head); ListNode right = SortList(mid); return Merge(left, right); } private ListNode GetMiddle(ListNode head) { ListNode slow = head, fast = head.next; while (fast != null && fast.next != null) { slow = slow.next; fast = fast.next.next; } ListNode mid = slow.next; slow.next = null; // Split the list into two halves return mid; } private ListNode Merge(ListNode left, ListNode right) { ListNode dummy = new ListNode(0); ListNode tail = dummy; while (left != null && right != null) { if (left.val < right.val) { tail.next = left; left = left.next; } else { tail.next = right; right = right.next; } tail = tail.next; } tail.next = left ?? right; // Append the remaining elements return dummy.next; } } ``` When I run this code with the input list `4 -> 2 -> 1 -> 3`, I expect the output to be `1 -> 2 -> 3 -> 4`, but instead, I get an incorrect order like `4 -> 1 -> 2 -> 3`. I've confirmed that the linked list is being split correctly, but I suspect the merging logic is where things are going awry. I've also checked for null references and boundary cases, but I'm not seeing any obvious errors. Is there something I'm missing in the merging process, or does my approach seem fundamentally flawed? Any insights or suggestions would be greatly appreciated! My development environment is macOS. This is my first time working with C# 3.11. Could this be a known issue?