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圆形链接列表是链接列表的变体，其中第一个元素指向最后一个元素，最后一个元素指向第一个元素。 单链表和双链表都可以制成循环链表。

用C实现 (Implementation in C)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
struct node {
   int data;
   int key;
   struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
bool isEmpty() {
   return head == NULL;
}
int length() {
   int length = 0;
   //if list is empty
   if(head == NULL) {
      return 0;
   }
   current = head->next;
   while(current != head) {
      length++;
      current = current->next;   
   }
   return length;
}
//insert link at the first location
void insertFirst(int key, int data) {
   //create a link
   struct node *link = (struct node*) malloc(sizeof(struct node));
   link->key = key;
   link->data = data;
   if (isEmpty()) {
      head = link;
      head->next = head;
   } else {
      //point it to old first node
      link->next = head;
      //point first to new first node
      head = link;
   }    
}
//delete first item
struct node * deleteFirst() {
   //save reference to first link
   struct node *tempLink = head;
   if(head->next == head) {  
      head = NULL;
      return tempLink;
   }     
   //mark next to first link as first 
   head = head->next;
   //return the deleted link
   return tempLink;
}
//display the list
void printList() {
   struct node *ptr = head;
   printf("\n[ ");
   //start from the beginning
   if(head != NULL) {
      while(ptr->next != ptr) {     
         printf("(%d,%d) ",ptr->key,ptr->data);
         ptr = ptr->next;
      }
   }
   printf(" ]");
}
void main() {
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56); 
   printf("Original List: "); 
   //print list
   printList();
   while(!isEmpty()) {            
      struct node *temp = deleteFirst();
      printf("\nDeleted value:");  
      printf("(%d,%d) ",temp->key,temp->data);
   }   
   printf("\nList after deleting all items: ");
   printList();   
}

如果我们编译并运行上面的程序，它将产生以下结果 -

输出 (Output)

Original List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20) ]
Deleted value:(6,56) 
Deleted value:(5,40) 
Deleted value:(4,1) 
Deleted value:(3,30) 
Deleted value:(2,20) 
Deleted value:(1,10) 
List after deleting all items: 
[ ]