diff --git a/src/exercise-21/task_queue.c b/src/exercise-21/task_queue.c
index 39dc2f6bd00c950ae80ed30450eb8e2527135f89..cdf82d4ec80428d92b2e89925b30e9e0b75314f8 100644
--- a/src/exercise-21/task_queue.c
+++ b/src/exercise-21/task_queue.c
@@ -44,7 +44,7 @@ reverse_task_queue_by_group (TaskNode *head, int k)
           tail = tail->next;
           if (tail == NULL)
             {
-              // 在这里填写代码
+              return hair->next;
             }
         }
 
@@ -55,12 +55,14 @@ reverse_task_queue_by_group (TaskNode *head, int k)
       while (prev != tail)
         {
           TaskNode *temp = p->next;
-          // 在这里填写代码
+          p->next = prev;
+          prev = p;
+          p = temp;
         }
 
       pre->next = tail;
-
-      // 在这里填写代码
+      
+      pre = head;
 
       head = next;
     }