双链接列表java反向函数错误

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我的双链接列表有问题,因为控制台输出错误的尾部!我把它缩小到我认为在我的反向功能中的错误!如果有人可以看一看并给我一些关于我做错了什么的指导,或者我如何设置我的尾巴,以便报告正确的变量!非常感谢你!可能是一个简单的错误,我错过了正常!

import java.util.*;
import java.lang.*;
public class DLList<E> implements List<E> {
    //Your implementation
    private DNode<E> head;
    private DNode<E> tail;
    private int size = 0;

    public DLList(E item){
        tail = head = new DNode<E>(item);
        size++;

    }

    public DLList(){
        head = tail = null;
        size = 0;
    }


  /** Remove all contents from the list, so it is once again
      empty. */
  public void clear(){
    head = tail = null;
    size = 0;
  }



  /** Insert an element at the given location. 
    * allows you to insert after the tail
    * @param item The element to be inserted. 
    */
    public void insert(int index, E item){
    if(index < 0 || index > size){
        throw new IndexOutOfBoundsException(Integer.toString(index));
    }
    if(index == 0) {
        addFirst(item);

    }   
    else if(index == size){
        add(item);
    }
    else{
        DNode<E> node = getNode(index -1);
        addAfter(node, item);
    }   

    }

    public void addFirst(E item){
        if(size == 0) {
            tail = head = new DNode<E>(item);
        }
        else{
            DNode<E> newNode = new DNode<E>(item, null, head);
            head.setPrev(newNode);
            head = newNode;
        }
        size++;
    }

    public void addAfter(DNode<E> node, E item){
        DNode<E> newNode = new DNode<E>(item, node, node.getNext());
        node.getNext().setPrev(newNode);
        node.setNext(newNode);
        size++;
    }


  /** Append an element at the end of the list.
   *  @param item The element to be appended.
   */
  public void add(E item){
      if(size == 0){
          tail = head = new DNode<E>(item);
      }
      else{
          DNode<E> newNode = new DNode<E>(item, tail, null);
          tail.setNext(newNode);
          tail = newNode;
      }
      size++;
  }


  /** 
  * Remove the  element at the given location.



  */
  public void remove(int index){
    if(index < 0 || index > size){
        throw new IndexOutOfBoundsException(Integer.toString(index));
    }
    if(index == 0) {
        removeFirst();
    }   
    else if(index == size){
        removeLast();
    }
    else{
        DNode<E> node = getNode(index -1);
        removeAfter(node);
    }   
  }

    public void removeFirst(){
        /*
    if(head == null){
        throw new NoSuchElementException("List is empty");
    }
    else if(head == tail){
        head = tail = null;
    }
    else{
        head= head.getNext();
        head.prev(item) = null;
    }

    */

    //setPrev
    DNode<E> temp = head;
    head = head.getNext();

    }

    public void removeLast(){
        /*
        if(head == null) {
            throw new NoSuchElementException("List is empty");
        }
        else if(head == tail){
            //RemoveFirst code
        }
        else{
            tail = tail.prev();
            tail.getNext() = null;
        }
        size--;
        */
        DNode<E> temp = tail;
        tail =  tail.getNext();
    }

  public void removeAfter(DNode<E> node){
      /*
    if(size == 0) {
            throw new IndexOutOfBoundsException(Integer.toString(index));
        }
        else if(head == tail){
            heal = tail = null;
        }
        else{
            head = head.getNext();
            head.prev = null;
        }
        size--;
        */

    DNode<E> temp = node.getNext();
  //Make sure value is  valid
  if (temp != null)
  {
    node.setNext(temp.getNext());
    size--;

  } 
  }



    public DNode<E> getNode(int index){
      if(index < 0 || index > size){
        throw new IndexOutOfBoundsException(Integer.toString(index));
    }
    DNode<E> node = head;
    for(int i = 0; i < index; i++) {
        node = node.getNext();
    } 
      return node;
  }

  /** 
  * Get the element in the position to one step left. 
  * @return element in the node to the left of the node at the index, 
  * null if at the head. 
  */  
  public E prev(int index){

      if (index < 0 || index >= size) {
    throw new IndexOutOfBoundsException(Integer.toString(index));
  }

  DNode<E> node = getNode(index-1);
      return node.getElement();
  }


  /** Get the element in the position one step right. 
  * @return the element in the node to the right of 
  * the node at the index, null if at the end. 
  */
  public E next(int index){
     if (index < 0 || index >= size) {
    throw new
        IndexOutOfBoundsException(Integer.toString(index));
  }
  DNode<E> node = getNode(index+1);
      return node.getElement();
  }


  /** @return The number of elements in the list. */
  public int length(){
      return size;
  }


   /** Turn the contents of the Nodes to a string in order from head to end.
   * @return The String representation of the 
   * elements in the list from head to end. 
   */
   //Copy and past prev but change symbol!
   public String toString(){
        DNode<E> node = head;
       String result = "";
       while(node != null) {
           result = result + node.getElement().toString();
           if(node.getNext() != null){
               result = result + " <==> ";
           }
           node = node.getNext();
       }
       return result; 
   }

   /** Reverse the content of the list.
    * if list is A => B => C it becomes C => B => A
    */
  public void reverse(){
      /*
      head.prev = head.getNext();
      head.getNext() = null;

      while(head.prev != null){
          head = head.prev;
          DNode<E> temp = head.getNext();
          head.getNext() = head.prev;
          head.prev = temp;
      }
      */
       DNode<E> node = head;
      if(node == null || node.getNext() == null){
          return;

      }

      DNode<E> prev = node.getNext();
      DNode<E> curr = prev.getNext();
        prev.setNext(node);
        node.setNext(null);     
      while (curr != null) {
         DNode<E> next = curr.getNext();
        curr.setNext(prev);
        prev = curr;
        curr = next;         
      }
      head = prev;






  }


  public E setprev(int index){
      if (index < 0 || index >= size) {
    throw new
        IndexOutOfBoundsException(Integer.toString(index));
  }
  DNode<E> node = getNode(index-1);
        return node.getElement();
  }

   /** @return The  element at given position. */
   public E getValue(int index){
       if (index < 0 || index >= size) {
        throw new
            IndexOutOfBoundsException(Integer.toString(index));
      }
      DNode<E> node = getNode(index);
      return node.getElement();
   }

   /**inserts the given list after the given index
   *Check if getNext is null
   *if(temp != null){
       (then set prev)
       {
 else{
       set tail list last value
   }
*/
    public void insertList (DLList list, int index){
        if (list.getHead() != null && (index >= 0 && index <size)){

            DNode<E> head = list.getHead();
            DNode<E> tail = list.getLast();

            DNode<E> position = getNode(index);
            DNode<E> temp= position.getNext(); 

            position.setNext(head);
            tail.setNext(temp);

            size = list.length()+ size;
        }

    }

    public DNode<E> getHead(){
        return head;
    }
    public DNode<E> getLast(){
        return tail;
    }

}
答案

从geeks获得了极客的代码,你只需要为你的变量名和节点的类名修改它。

 void reverse() { 
    Node temp = null; 
    Node current = head; 

    /* swap next and prev for all nodes of  
     doubly linked list */
    while (current != null) { 
        temp = current.prev; 
        current.prev = current.next; 
        current.next = temp; 
        current = current.prev; 
    } 

    /* Before changing head, check for the cases like empty  
     list and list with only one node */
    if (temp != null) { 
        head = temp.prev; 
    } 
} 

如果您有任何疑问,请随时提出。

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