添加C#版

problems/0019.删除链表的倒数第N个节点.md

@@ -412,6 +412,28 @@ struct ListNode* removeNthFromEnd(struct ListNode* head, int n) {
 
 ```
 
+C#：
+```csharp
+public class Solution {
+    public ListNode RemoveNthFromEnd(ListNode head, int n) {
+        ListNode dummpHead = new ListNode(0);
+        dummpHead.next = head;
+        var fastNode = dummpHead;
+        var slowNode = dummpHead;
+        while(n-- != 0 && fastNode != null)
+        {
+            fastNode = fastNode.next;
+        }
+        while(fastNode.next != null)
+        {
+            fastNode = fastNode.next;
+            slowNode = slowNode.next;
+        }
+        slowNode.next = slowNode.next.next;
+        return dummpHead.next;
+    }
+}
+```
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