将单向链表转换为循环链表

给定一个单向链表，我们必须将其转换为循环链表。例如，我们得到了一个有四个节点的单向链表，我们想把这个单向链表转换成循环链表。

上面的单链表转化为循环链表。

方法：思路是遍历单向链表，检查该节点是否为最后一个节点。如果该节点是最后一个节点，即指向 NULL，则使其指向起始节点，即头节点。下面是这个方法的实现。

C++

// Program for converting singly linked list
// into circular linked list.
#include 
 
/* Linked list node */
struct Node {
    int data;
    struct Node* next;
};
 
// Function that convert singly linked list
// into circular linked list.
struct Node* circular(struct Node* head)
{
    // declare a node variable start and
    // assign head node into start node.
    struct Node* start = head;
 
    // check that while head->next not equal
    // to NULL then head points to next node.
    while (head->next != NULL)
        head = head->next;
         
    // if head->next points to NULL then
    // start assign to the head->next node.
    head->next = start;
    return start;
}
 
void push(struct Node** head, int data)
{
    // Allocate dynamic memory for newNode.
    struct Node* newNode = (struct Node*)malloc
                          (sizeof(struct Node));
 
    // Assign the data into newNode.
    newNode->data = data;
 
    // newNode->next assign the address of
    // head node.
    newNode->next = (*head);
 
    // newNode become the headNode.
    (*head) = newNode;
}
 
// Function that display the elements of
// circular linked list.
void displayList(struct Node* node)
{
    struct Node* start = node;
 
    while (node->next != start) {
        printf("%d ", node->data);
        node = node->next;
    }
     
    // Display the last node of circular
    // linked list.
    printf("%d ", node->data);
}
 
// Driver program to test the functions
int main()
{
    // Start with empty list
    struct Node* head = NULL;
 
    // Using push() function to construct
    // singly linked list
    // 17->22->13->14->15
    push(&head, 15);
    push(&head, 14);
    push(&head, 13);
    push(&head, 22);
    push(&head, 17);
 
    // Call the circular_list function that
    // convert singly linked list to circular
    // linked list.
    circular(head);
 
    printf("Display list: \n");
    displayList(head);
 
    return 0;
}

Java

// Program for converting
// singly linked list into
// circular linked list.
class GFG
{
 
/*Linked list node */
static class Node
{
    int data;
    Node next;
};
 
// Function that convert
// singly linked list into
// circular linked list.
static Node circular(Node head)
{
    // declare a node variable
    // start and assign head
    // node into start node.
    Node start = head;
 
    // check that while head.next
    // not equal to null then head
    // points to next node.
    while (head.next != null)
        head = head.next;
         
    // if head.next points to null
    // then start assign to the
    // head.next node.
    head.next = start;
    return start;
}
 
static Node push(Node head, int data)
{
    // Allocate dynamic memory
    // for newNode.
    Node newNode = new Node();
 
    // Assign the data into newNode.
    newNode.data = data;
 
    // newNode.next assign the
    // address of head node.
    newNode.next = (head);
 
    // newNode become the headNode.
    (head) = newNode;
     
    return head;
}
 
// Function that display the elements
// of circular linked list.
static void displayList( Node node)
{
    Node start = node;
 
    while (node.next != start)
    {
        System.out.print(" "+ node.data);
        node = node.next;
    }
     
    // Display the last node of 
    // circular linked list.
    System.out.print(" " + node.data);
}
 
// Driver Code
public static void main(String args[])
{
    // Start with empty list
    Node head = null;
 
    // Using push() function to
    // convert singly linked list
    // 17.22.13.14.15
    head = push(head, 15);
    head = push(head, 14);
    head = push(head, 13);
    head = push(head, 22);
    head = push(head, 17);
 
    // Call the circular_list function
    // that converst singly linked
    // list to circular linked list.
    circular(head);
 
    System.out.print("Display list: \n");
    displayList(head);
}
}
 
// This code is contributed
// by Arnab Kundu

Python3

# Python3 program for converting
# singly linked list into
# circular linked list.
import sys
 
# Linked list node
class Node:
    def __init__(self,data):
        self.data = data
        self.next = None
 
def push(head, data):
    if not head:
        return Node(data)
 
    # Allocate dynamic memory
    # for newNode.
    # Assign the data into newNode.
    newNode = Node(data)
 
    # newNode.next assign the
    # address of head node.
    newNode.next = head
 
    # newNode become the headNode.
    head = newNode
    return head
 
# Function that convert
# singly linked list into
# circular linked list.
def circular(head):
 
    # declare a node variable
    # start and assign head
    # node into start node.
    start = head
 
    # check that while head.next
    # not equal to null then head
    # points to next node.
    while(head.next is not None):
        head = head.next
 
    # if head.next points to null
    # then start assign to the
    # head.next node.    
    head.next = start
    return start
 
# Function that display the elements
# of circular linked list.
def displayList(node):
    start = node
    while(node.next is not start):
        print("{} ".format(node.data),end="")
        node=node.next
 
    # Display the last node of
    # circular linked list.
    print("{} ".format(node.data),end="")
 
# Driver Code
if __name__=='__main__':
     
    # Start with empty list
    head=None
 
    # Using push() function to
    # convert singly linked list
    # 17.22.13.14.15
    head=push(head,15)
    head=push(head,14)
    head=push(head,13)
    head=push(head,22)
    head=push(head,17)
 
    # Call the circular_list function
    # that converst singly linked
    # list to circular linked list.
    circular(head)
    print("Display List:")
    displayList(head)
 
# This Code is Contributed By Vikash Kumar 37

C#

// C# Program for converting
// singly linked list into
// circular linked list.
using System;
 
class GFG
{
 
    /*Linked list node */
    public class Node
    {
        public int data;
        public Node next;
    };
 
    // Function that convert
    // singly linked list into
    // circular linked list.
    static Node circular(Node head)
    {
        // declare a node variable
        // start and assign head
        // node into start node.
        Node start = head;
 
        // check that while head.next
        // not equal to null then head
        // points to next node.
        while (head.next != null)
            head = head.next;
 
        // if head.next points to null
        // then start assign to the
        // head.next node.
        head.next = start;
        return start;
    }
 
    static Node push(Node head, int data)
    {
        // Allocate dynamic memory
        // for newNode.
        Node newNode = new Node();
 
        // Assign the data into newNode.
        newNode.data = data;
 
        // newNode.next assign the
        // address of head node.
        newNode.next = (head);
 
        // newNode become the headNode.
        (head) = newNode;
 
        return head;
    }
 
    // Function that display the elements
    // of circular linked list.
    static void displayList( Node node)
    {
        Node start = node;
 
        while (node.next != start)
        {
            Console.Write(" " + node.data);
            node = node.next;
        }
 
        // Display the last node of
        // circular linked list.
        Console.Write(" " + node.data);
    }
 
    // Driver Code
    public static void Main(String []args)
    {
        // Start with empty list
        Node head = null;
 
        // Using push() function to
        // convert singly linked list
        // 17.22.13.14.15
        head = push(head, 15);
        head = push(head, 14);
        head = push(head, 13);
        head = push(head, 22);
        head = push(head, 17);
 
        // Call the circular_list function
        // that converst singly linked
        // list to circular linked list.
        circular(head);
 
        Console.Write("Display list: \n");
        displayList(head);
    }
}
 
// This code is contributed 29AjayKumar

Javascript

// Javascript Program for converting
// singly linked list into
// circular linked list.    /* Linked list node */
class Node
{
        constructor(val)
        {
            this.data = val;
            this.next = null;
        }
    }
 
    // Function that convert
    // singly linked list into
    // circular linked list.
    function circular( head)
    {
     
        // declare a node variable
        // start and assign head
        // node into start node.
         start = head;
 
        // check that while head.next
        // not equal to null then head
        // points to next node.
        while (head.next != null)
            head = head.next;
 
        // if head.next points to null
        // then start assign to the
        // head.next node.
        head.next = start;
        return start;
    }
 
    function push( head , data)
    {
     
        // Allocate dynamic memory
        // for newNode.
         newNode = new Node();
 
        // Assign the data into newNode.
        newNode.data = data;
 
        // newNode.next assign the
        // address of head node.
        newNode.next = (head);
 
        // newNode become the headNode.
        (head) = newNode;
 
        return head;
    }
 
    // Function that display the elements
    // of circular linked list.
    function displayList( node)
    {
         start = node;
 
        while (node.next != start)
        {
            document.write(" " + node.data);
            node = node.next;
        }
 
        // Display the last node of
        // circular linked list.
        document.write(" " + node.data);
    }
 
    // Driver Code
     
        // Start with empty list
         head = null;
 
        // Using push() function to
        // convert singly linked list
        // 17.22.13.14.15
        head = push(head, 15);
        head = push(head, 14);
        head = push(head, 13);
        head = push(head, 22);
        head = push(head, 17);
 
        // Call the circular_list function
        // that converst singly linked
        // list to circular linked list.
        circular(head);
 
        document.write("Display list: <br/>");
        displayList(head);
 
// This code is contributed by gauravrajput1

输出：

Display list:
17 22 13 14 15

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