create 0148-sort-list.cs

Author: NotADucc

Diff for: csharp/0148-sort-list.cs

@@ -0,0 +1,49 @@
+public class Solution 
+{
+    public ListNode SortList(ListNode head)
+    {
+        if (head is null || head.next is null) 
+            return head;
+
+        ListNode middle = GetMiddle(head);
+        ListNode left = head;
+        ListNode right = middle.next;
+        middle.next = null;
+
+        return Merge(SortList(left), SortList(right));
+    }
+    private ListNode GetMiddle(ListNode head)
+    {
+        ListNode slow = head;
+        ListNode fast = head.next;
+        while (fast != null && fast.next != null)
+        {
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        return slow;
+    }
+    private ListNode Merge(ListNode left, ListNode right)
+    {
+        var head = new ListNode();
+        var tail = head;
+        while (left is not null && right is not 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 is not null ? left : right!;
+
+        return head.next;
+    }
+}