单链表反转(Singly Linked Lists in Java)

最新推荐文章于 2025-08-22 13:45:39 发布

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#java #数据结构与算法

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本文介绍了一种使用递归方法来反转单链表的实现方式。通过定义一个递归函数，该函数接受链表头节点作为参数，并返回反转后的链表头节点。此外，还提供了一个用于生成测试用例的辅助函数以及链表类的实现。

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package dsa.linkedlist;

public class Node<E>{
 E data;
 Node<E> next;
}

package dsa.linkedlist;

public class ReverseLinkedListRecursively {

	public static void main(String args[]) {
		ReverseLinkedListRecursively reverser = new ReverseLinkedListRecursively();
		SinglyLinkedList<Integer> originalList = reverser.getLabRatList(10);
		System.out.println("Original List : " + originalList.toString());
		originalList.start = reverser.reverse(originalList.start);
		System.out.println("Reversed List : " + originalList.toString());
	}

	public Node<Integer> reverse(Node<Integer> list) {
		if (list == null || list.next == null)
			return list;
		Node<Integer> nextItem = list.next;
		list.next = null;
		Node<Integer> reverseRest = reverse(nextItem);
		nextItem.next = list;
		return reverseRest;
	}

	private SinglyLinkedList<Integer> getLabRatList(int count) {
		SinglyLinkedList<Integer> sampleList = new SinglyLinkedList<Integer>();
		for (int i = 0; i < count; i++) {
			sampleList.add(i);
		}
		return sampleList;
	}
}
/*
 * SAMPLE OUTPUT Original List : 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 Reversed List : 9,
 * 8, 7, 6, 5, 4, 3, 2, 1, 0
 */

package dsa.linkedlist;

/**
 * This is a singly linked list with no prev pointer.
 * @author Braga
 * @param <E>
 */
public class SinglyLinkedList<E> {
 
 Node<E> start;
 int size;
 
 public SinglyLinkedList(){
  start = null;
  size = 0;
 }
 
 //insertAtLast
 public void add(E data){
  insertAtLast(data);
 }
 
 public void insertAtLast(E data){
  if(size==0){
   start = new Node<E>();
   start.next = null;
   start.data = data;
  }else{
   Node<E> currentNode = getNodeAt(size-1);
   Node<E> newNode = new Node<E>();
   newNode.data = data;
   newNode.next = null;
   currentNode.next = newNode;
  }
  size++;
 }
 
 public void insertAtFirst(E data){
  if(size==0){
   start = new Node<E>();
   start.next = null;
   start.data = data;
  }else{
   Node<E> newNode = new Node<E>();
   newNode.data = data;
   newNode.next = start;
   start = newNode;
  }
  size++;
 }
 
 public Node<E> getNodeAt(int nodePos) throws ArrayIndexOutOfBoundsException{
  if(nodePos>=size || nodePos<0){
   throw new ArrayIndexOutOfBoundsException();
  }
  Node<E> temp = start;//Move pointer to front
  int counter = 0;
  for(;counter<nodePos;counter++){
   temp = temp.next;
  }
  return temp;
 }
 
 public void insertAt(int position, E data){
  if(position == 0){
   insertAtFirst(data);
  }else if(position==size-1){
   insertAtLast(data);
  }else{
   Node<E> tempNode = getNodeAt(position-1);
   Node<E> newNode = new Node<E>();
   newNode.data = data;
   newNode.next = tempNode.next;
   tempNode.next = newNode;
   size++;
  }
 }
 
 public Node<E> getFirst(){
  return getNodeAt(0);
 }
 
 public Node<E> getLast(){
  return getNodeAt(size-1);
 }
 
 public E removeAtFirst(){
  if(size==0){
   throw new ArrayIndexOutOfBoundsException();
  }
  E data = start.data;
  start = start.next;
  size--;
  return data;
 }
 
 public E removeAtLast(){
  if(size==0){
   throw new ArrayIndexOutOfBoundsException();
  }
  Node<E> tempNode = getNodeAt(size-2);
  E data = tempNode.next.data;
  tempNode.next = null;
  size--;
  return data;
 }
 
 public E removeAt(int position){
  if(position==0){
   return removeAtFirst();
  }else if(position == size-1){
   return removeAtLast();
  }else{
   Node<E> tempNode = getNodeAt(position-1);
   E data = tempNode.next.data;
   tempNode.next = tempNode.next.next;
   size--;
   return data;
  }
 }
 
 public int size(){
  return size;
 }
 
 public String toString(){
  if(size==0){
   return "";
  }else{
   StringBuilder output = new StringBuilder();
   Node<E> tempNode = start;
   while(tempNode.next!=null){
    output.append(tempNode.data).append(", ");
    tempNode = tempNode.next;
   }
   output.append(tempNode.data);
   return output.toString();
  }
 }
 
}