循环链表数据结构

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什么是循环链表？

循环链表是链表的一种变体，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转换为循环链表。

单链表作为循环链表

在单链表中，最后一个节点的next指针指向第一个节点。

Singly Linked List As Circular

双链表作为循环链表

在双链表中，最后一个节点的next指针指向第一个节点，第一个节点的prev指针指向最后一个节点，从而构成双向循环。

Doubly Linked List As Circular

根据以上说明，需要考虑以下几点：

  • 在单链表和双链表的情况下，最后一个链接的next指针都指向列表的第一个链接。

  • 在双链表的情况下，第一个链接的prev指针指向列表的最后一个链接。

循环链表的基本操作

以下是循环链表支持的重要操作：

  • 插入 - 在列表的开头插入一个元素。

  • 删除 - 从列表的开头删除一个元素。

  • 显示 - 显示列表。

循环链表 - 插入操作

循环链表的插入操作只在列表的开头插入元素。这与普通的单链表和双链表不同，因为此列表没有特定的起点和终点。插入操作可以在开头进行，也可以在特定节点（或给定位置）之后进行。

算法

1. START
2. Check if the list is empty
3. If the list is empty, add the node and point the head 
   to this node
4. If the list is not empty, link the existing head as 
   the next node to the new node.
5. Make the new node as the new head.
6. END

示例

以下是此操作在各种编程语言中的实现：

C C++ Java Python
#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;
}

//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;
   }
}

//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("Circular Linked List: ");

   //print list
   printList();
}

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20)  ]

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdbool>
struct node {
   int data;
   int key;
   struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
bool isEmpty(){
   return head == NULL;
}
//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;
   }
}

//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(" ]");
}
int main(){
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56);
   printf("Circular Linked List: ");
   
   //print list
   printList();
   return 0;
}

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20)  ]

//Java program for circular link list
import java.util.*;
class Node {
    int data;
    int key;
    Node next;
}
public class Main {
    static Node head = null;
    static Node current = null;
    static boolean isEmpty() {
        return head == null;
    }
    //insert link at the first location
    static void insertFirst(int key, int data) {
        //create a link
        Node link = new 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;
        }
    }
    //display the list
    static void printList() {
        Node ptr = head;
        System.out.print("\n[ ");
        //start from the beginning
        if (head != null) {
            while (ptr.next != ptr) {
                System.out.print("(" + ptr.key + "," + ptr.data + ") ");
                ptr = ptr.next;
            }
        }
        System.out.print(" ]");
    }
    public static void main(String[] args) {
        insertFirst(1, 10);
        insertFirst(2, 20);
        insertFirst(3, 30);
        insertFirst(4, 1);
        insertFirst(5, 40);
        insertFirst(6, 56);
        System.out.print("Circular Linked List: ");
        //print list
        printList();
    }
}

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20) ]

#python program for circular linked list
class Node:
    def __init__(self, key, data):
        self.key = key
        self.data = data
        self.next = None
head = None
current = None
def is_empty():
    return head is None
#insert link at the first location
def insert_first(key, data):
    #create a link
    global head
    new_node = Node(key, data)
    if is_empty():
        head = new_node
        head.next = head
    else:
        #point it to old first node
        new_node.next = head
        #point first to the new first node
        head = new_node
        #display the list
def print_list():
    global head
    ptr = head
    print("[", end=" ")
    #start from the beginning
    if head is not None:
        while ptr.next != ptr:
            print("({}, {})".format(ptr.key, ptr.data), end=" ")
            ptr = ptr.next
        print("]")
insert_first(1, 10)
insert_first(2, 20)
insert_first(3, 30)
insert_first(4, 1)
insert_first(5, 40)
insert_first(6, 56)
#printlist
print("Circular Linked List: ")
print_list()

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20) ]

循环链表 - 删除操作

循环链表的删除操作是从列表中删除某个节点。此类列表中的删除操作可以在开头、给定位置或结尾进行。

算法

1. START
2. If the list is empty, then the program is returned.
3. If the list is not empty, we traverse the list using a 
   current pointer that is set to the head pointer and create 
   another pointer previous that points to the last node.
4. Suppose the list has only one node, the node is deleted 
   by setting the head pointer to NULL.
5. If the list has more than one node and the first node is to 
   be deleted, the head is set to the next node and the previous
   is linked to the new head.
6. If the node to be deleted is the last node, link the preceding 
   node of the last node to head node.
7. If the node is neither first nor last, remove the node by 
   linking its preceding node to its succeeding node.
8. END

示例

以下是此操作在各种编程语言中的实现：

C C++ Java Python
#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;
}

//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;

   //start from the beginning
   if(head != NULL) {
      while(ptr->next != ptr) {
         printf("(%d,%d) ",ptr->key,ptr->data);
         ptr = ptr->next;
      }
   }
}
void main(){
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56);
   printf("Circular Linked List: ");

   //print list
   printList();
   deleteFirst();
   printf("\nList after deleting the first item: ");
   printList();
}

输出

Circular Linked List: (6,56) (5,40) (4,1) (3,30) (2,20) 
List after deleting the first item: (5,40) (4,1) (3,30) (2,20) 

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdbool>
struct node {
   int data;
   int key;
   struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
bool isEmpty(){
   return head == NULL;
}

//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;

   //start from the beginning
   if(head != NULL) {
      while(ptr->next != ptr) {
         printf("(%d,%d) ",ptr->key,ptr->data);
         ptr = ptr->next;
      }
   }
}
int main(){
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56);
   printf("Circular Linked List: ");

   //print list
   printList();
   deleteFirst();
   printf("\nList after deleting the first item: ");
   printList();
   return 0;
}

输出

Circular Linked List: (6,56) (5,40) (4,1) (3,30) (2,20) 
List after deleting the first item: (5,40) (4,1) (3,30) (2,20) 

//Java program for circular linked list
import java.util.*;
public class Main {
    static class Node {
        int data;
        int key;
        Node next;
    }
    static Node head = null;
    static Node current = null;

    static boolean isEmpty() {
        return head == null;
    }
    //insert link at the first location
    static void insertFirst(int key, int data) {
        //create a link
        Node link = new 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
    static Node deleteFirst() {
        //save reference to first link
        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
    static void printList() {
        Node ptr = head;
         //start from the beginning
        if (head != null) {
            while (ptr.next != ptr) {
                System.out.printf("(%d,%d) ", ptr.key, ptr.data);
                ptr = ptr.next;
            }
        }
    }
    public static void main(String[] args) {
        insertFirst(1, 10);
        insertFirst(2, 20);
        insertFirst(3, 30);
        insertFirst(4, 1);
        insertFirst(5, 40);
        insertFirst(6, 56);
        System.out.print("Circular Linked List: ");
        //print list
        printList();
        deleteFirst();
		System.out.print("\nList after deleting the first item: ");
        printList();
  }
}

输出

Circular Linked List: (6,56) (5,40) (4,1) (3,30) (2,20) 
List after deleting the first item: (5,40) (4,1) (3,30) (2,20)

#python program for circular linked list
class Node:
    def __init__(self, key, data):
        self.key = key
        self.data = data
        self.next = None
head = None
current = None
def is_empty():
    return head is None
#insert link at the first location
def insert_first(key, data):
    #create a link
    global head
    new_node = Node(key, data)
    if is_empty():
        head = new_node
        head.next = head
    else:
        #point it to old first node
        new_node.next = head
        #point first to the new first node
        head = new_node
        
def print_list():
    global head
    ptr = head
    print("[", end=" ")
    #start from the beginning
    if head is not None:
        while ptr.next != ptr:
            print("({}, {})".format(ptr.key, ptr.data), end=" ")
            ptr = ptr.next
        print("]")
def delete_first():
    global head
    temp_link = head
    if head.next == head:
        head = None
        return temp_link
    head = head.next
    return temp_link  
insert_first(1, 10)
insert_first(2, 20)
insert_first(3, 30)
insert_first(4, 1)
insert_first(5, 40)
insert_first(6, 56)
#printlist
print("Circular Linked List: ")
print_list()
delete_first()
print("\nList after deleting the first item: ")
print_list();

输出

Circular Linked List: 
[ (6, 56) (5, 40) (4, 1) (3, 30) (2, 20) ]

List after deleting the first item: 
[ (5, 40) (4, 1) (3, 30) (2, 20) ]

循环链表 - 显示列表

显示列表操作访问列表中的每个节点，并将它们全部打印到输出中。

算法

1. START
2. Walk through all the nodes of the list and print them
3. END

示例

以下是此操作在各种编程语言中的实现：

C C++ Java Python
#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;
}

//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;
   }
}

//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("Circular Linked List: ");

   //print list
   printList();
}

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20)  ]

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdbool>
struct node {
   int data;
   int key;
   struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
bool isEmpty(){
   return head == NULL;
}

//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;
   }
}

//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(" ]");
}
int main(){
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56);
   printf("Circular Linked List: ");

   //print list
   printList();
   return 0;
}

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20)  ]

//Java program for circular link list
import java.util.*;
class Node {
    int data;
    int key;
    Node next;
}
public class Main {
    static Node head = null;
    static Node current = null;
    static boolean isEmpty() {
        return head == null;
    }
    //insert link at the first location
    static void insertFirst(int key, int data) {
        //create a link
        Node link = new 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;
        }
    }
    //display the list
    static void printList() {
        Node ptr = head;
        System.out.print("\n[ ");
        //start from the beginning
        if (head != null) {
            while (ptr.next != ptr) {
                System.out.print("(" + ptr.key + "," + ptr.data + ") ");
                ptr = ptr.next;
            }
        }
        System.out.print(" ]");
    }
    public static void main(String[] args) {
        insertFirst(1, 10);
        insertFirst(2, 20);
        insertFirst(3, 30);
        insertFirst(4, 1);
        insertFirst(5, 40);
        insertFirst(6, 56);
        System.out.print("Circular Linked List: ");
        //print list
        printList();
    }
}

输出

Circular Linked List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20) ]

#python program for circular linked list
class Node:
    def __init__(self, key, data):
        self.key = key
        self.data = data
        self.next = None
head = None
current = None
def is_empty():
    return head is None
#insert link at the first location
def insert_first(key, data):
    #create a link
    global head
    new_node = Node(key, data)
    if is_empty():
        head = new_node
        head.next = head
    else:
        #point it to old first node
        new_node.next = head
        #point first to the new first node
        head = new_node
        #display the list
def print_list():
    global head
    ptr = head
    print("[", end=" ")
    #start from the beginning
    if head is not None:
        while ptr.next != ptr:
            print("({}, {})".format(ptr.key, ptr.data), end=" ")
            ptr = ptr.next
        print("]")
insert_first(1, 10)
insert_first(2, 20)
insert_first(3, 30)
insert_first(4, 1)
insert_first(5, 40)
insert_first(6, 56)
#printlist
print("Circular Linked List: ")
print_list()

输出

Circular Linked List: [ (6,56) (5,40) (4,1) (3,30) (2,20) ]

循环链表 - 完整实现

以下是循环链表在各种编程语言中的完整实现：

C C++ Java Python
#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(" ]");
}
int 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();
}

输出

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: 
[  ]

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdbool>
using namespace std;
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;
   cout << "\n[ ";
   //start from the beginning
   if(head != NULL) {
      while(ptr->next != ptr) {
         cout << "(" << ptr->key << "," << ptr->data << ") ";
         ptr = ptr->next;
      }
   }
   cout << " ]";
}
int main(){
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56);
   cout << "Original List: ";
   //print list
   printList();
   while(!isEmpty()) {
      struct node *temp = deleteFirst();
      cout << "\n Deleted value:";
      cout << "(" << temp->key << "," << temp->data << ") ";
   }
   cout << "\n List after deleting all items: ";
   printList();
   return 0;
}

输出

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: 
[  ]

class Node {
    int data;
    int key;
    Node next;
    Node(int key, int data) {
        this.key = key;
        this.data = data;
        this.next = null;
    }
}
public class LinkedList {
    private Node head;
    private Node current;
    boolean 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
        Node link = new Node(key, 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
    Node deleteFirst() {
        if (head.next == head) {
            //save reference to first link
            Node tempLink = head;
            head = null;
            return tempLink;
        }
        Node tempLink = head;
        //mark next to first link as first
        head = head.next;
        //return the deleted link
        return tempLink;
    }
    //display the list
    void printList() {
        Node ptr = head;
        System.out.print("\n[ ");

        //start from the beginning
        if (head != null) {
            while (ptr.next != ptr) {
                System.out.print("(" + ptr.key + "," + ptr.data + ") ");
                ptr = ptr.next;
            }
        }
        System.out.print(" ]");
    }
    public static void main(String[] args) {
        LinkedList linkedList = new LinkedList();
        linkedList.insertFirst(1, 10);
        linkedList.insertFirst(2, 20);
        linkedList.insertFirst(3, 30);
        linkedList.insertFirst(4, 1);
        linkedList.insertFirst(5, 40);
        linkedList.insertFirst(6, 56);
        System.out.print("Original List: ");
        linkedList.printList();
        //print list
        while (!linkedList.isEmpty()) {
            Node temp = linkedList.deleteFirst();
            System.out.println("\nDeleted value: (" + temp.key + "," + temp.data + ")");
        }
        System.out.print("\nList after deleting all items: ");
        linkedList.printList();
    }
}

输出

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: 
[  ]

class Node:
    def __init__(self, key, data):
        self.key = key
        self.data = data
        self.next = None
class LinkedList:
    def __init__(self):
        self.head = None
        self.current = None
    def is_empty(self):
        return self.head is None
    def length(self):
        length = 0
        # If list is empty
        if self.head is None:
            return 0
        self.current = self.head.next
        while self.current != self.head:
            length += 1
            self.current = self.current.next
        return length
    # insert link at the first location
    def insert_first(self, key, data):
        # create a link
        new_node = Node(key, data)
        if self.is_empty():
            self.head = new_node
            self.head.next = self.head
        else:
            # point it to old first node
            new_node.next = self.head
            # point first to new first node
            self.head = new_node
    # delete first item
    def delete_first(self):
        # save reference to first link
        if self.head.next == self.head:
            temp_link = self.head
            self.head = None
            return temp_link
        # mark next to first link as first
        temp_link = self.head
        self.head = self.head.next
        # return the deleted link
        return temp_link
    # Diplay the list
    def print_list(self):
        ptr = self.head
        print("[", end=" ")
        # start from the beginning
        if self.head is not None:
            while ptr.next != ptr:
                print("({}, {})".format(ptr.key, ptr.data), end=" ")
                ptr = ptr.next
        print("]")
# Main function
if __name__ == '__main__':
    linked_list = LinkedList()
    linked_list.insert_first(1, 10)
    linked_list.insert_first(2, 20)
    linked_list.insert_first(3, 30)
    linked_list.insert_first(4, 1)
    linked_list.insert_first(5, 40)
    linked_list.insert_first(6, 56)
    print("Original List: ", end="")
    linked_list.print_list()
    while not linked_list.is_empty():
        temp = linked_list.delete_first()
        print("\nDeleted value: ({}, {})".format(temp.key, temp.data))
    # print list
    print("List after deleting all items: ", end="")
    linked_list.print_list()

输出

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: [ ]
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