cs: add “206. Reverse Linked List”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/reverse-linked-list.cs

@@ -0,0 +1,25 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public int val;
+ *     public ListNode next;
+ *     public ListNode(int val=0, ListNode next=null) {
+ *         this.val = val;
+ *         this.next = next;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode ReverseList(ListNode head) {
+        ListNode next = null;
+
+        while (head != null) {
+            var toRight = head.next;
+            head.next = next;
+            next = head;
+            head = toRight;
+        }
+
+        return next;
+    }
+}