反向链表的Java程序

给定指向链表头节点的指针，任务是反转链表。我们需要通过改变节点之间的链接来反转列表。

例子：

Input : Head of following linked list  
       1->2->3->4->NULL
Output : Linked list should be changed to,
       4->3->2->1->NULL

Input : Head of following linked list  
       1->2->3->4->5->NULL
Output : Linked list should be changed to,
       5->4->3->2->1->NULL

Input : NULL
Output : NULL

Input  : 1->NULL
Output : 1->NULL

迭代法

Java

// Java program for reversing the linked list
  
class LinkedList {
  
    static Node head;
  
    static class Node {
  
        int data;
        Node next;
  
        Node(int d) {
            data = d;
            next = null;
        }
    }
  
    /* Function to reverse the linked list */
    Node reverse(Node node) {
        Node prev = null;
        Node current = node;
        Node next = null;
        while (current != null) {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        node = prev;
        return node;
    }
  
    // prints content of double linked list
    void printList(Node node) {
        while (node != null) {
            System.out.print(node.data + " ");
            node = node.next;
        }
    }
  
    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.head = new Node(85);
        list.head.next = new Node(15);
        list.head.next.next = new Node(4);
        list.head.next.next.next = new Node(20);
          
        System.out.println("Given Linked list");
        list.printList(head);
        head = list.reverse(head);
        System.out.println("");
        System.out.println("Reversed linked list ");
        list.printList(head);
    }
}
  
  
// This code has been contributed by Mayank Jaiswal
Recursive Method:void recursiveReverse(struct Node** head_ref)
{
    struct Node* first;
    struct Node* rest;
       
    /* empty list */
    if (*head_ref == NULL)
       return;   
  
    /* suppose first = {1, 2, 3}, rest = {2, 3} */
    first = *head_ref;  
    rest  = first->next;
  
    /* List has only one node */
    if (rest == NULL)
       return;   
  
    /* reverse the rest list and put the first element at the end */
    recursiveReverse(&rest);
    first->next->next  = first;  
      
    /* tricky step -- see the diagram */
    first->next  = NULL;          
  
    /* fix the head pointer */
    *head_ref = rest;              
}
A Simpler and Tail Recursive Method

Java

// Java program for reversing the Linked list
  
class LinkedList {
  
    static Node head;
  
    static class Node {
  
        int data;
        Node next;
  
        Node(int d) {
            data = d;
            next = null;
        }
    }
  
    // A simple and tail recursive function to reverse
    // a linked list.  prev is passed as NULL initially.
    Node reverseUtil(Node curr, Node prev) {
  
        /* If last node mark it head*/
        if (curr.next == null) {
            head = curr;
  
            /* Update next to prev node */
            curr.next = prev;
            return null;
        }
  
        /* Save curr->next node for recursive call */
        Node next1 = curr.next;
  
        /* and update next ..*/
        curr.next = prev;
  
        reverseUtil(next1, curr);
        return head;
    }
  
    // prints content of double linked list
    void printList(Node node) {
        while (node != null) {
            System.out.print(node.data + " ");
            node = node.next;
        }
    }
  
    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.head = new Node(1);
        list.head.next = new Node(2);
        list.head.next.next = new Node(3);
        list.head.next.next.next = new Node(4);
        list.head.next.next.next.next = new Node(5);
        list.head.next.next.next.next.next = new Node(6);
        list.head.next.next.next.next.next.next = new Node(7);
        list.head.next.next.next.next.next.next.next = new Node(8);
  
        System.out.println("Original Linked list ");
        list.printList(head);
        Node res = list.reverseUtil(head, null);
        System.out.println("");
        System.out.println("");
        System.out.println("Reversed linked list ");
        list.printList(res);
    }
}
// This code has been contributed by Mayank Jaiswal
Please refer complete article on Reverse a linked list for more details!In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.