数据结构循环链接列表

#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();   

}