使用带尾指针的链表实现队列

使用带尾指针的链表实现队列

  1. 普通链表在头部删除和添加节点是快速的,但是在尾部操作时间复杂度过高。如果要实现队列,则带尾指针的链表可以解决在尾部操作时间复杂度的问题。入队与出队的时间复杂度都为O(1)。

  2. 具体实现代码

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package LinkedList.LinkedListQueue;

/**
* @ Description: 使用链表实现队列
* @ Date: Created in 14:04 12/07/2018
* @ Author: Anthony_Duan
*/
public class LinkedListQueue<E> implements Queue<E> {

private class Node {
public E e;
public Node next;

public Node(E e, Node next) {
this.e = e;
this.next = next;
}

public Node(E e) {
this(e, null);
}

public Node() {
this(null, null);
}

@Override
public String toString() {
return e.toString();
}
}

private Node head, tail;
private int size;

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

@Override
public int getSize() {
return size;
}

@Override
public boolean isEmpty() {
return size == 0;
}

@Override
public void enqueue(E e) {
if (tail == null) {
tail = new Node(e);
head = tail;
} else {
tail.next = new Node(e);
tail = tail.next;
}
size++;
}


@Override
public E dequeue() {
if (isEmpty()) {
throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
}
Node retNode = head;
head = head.next;
retNode.next = null;
if (head == null) {
tail = null;
}
size--;
return retNode.e;
}

@Override
public E getFront() {
if (isEmpty()) {
throw new IllegalArgumentException("Queue is empty.");
}
return head.e;
}

@Override
public String toString() {
StringBuilder res = new StringBuilder();
res.append("Queue: front ");

Node cur = head;
while (cur != null) {
res.append(cur + "->");
cur = cur.next;
}
res.append("NULL tail");
return res.toString();
}


public static void main(String[] args) {
LinkedListQueue<Integer> queue = new LinkedListQueue<Integer>();
for (int i = 0; i < 10; i++) {
queue.enqueue(i);
System.out.println(queue);

if (i % 3 == 2) {
queue.dequeue();
System.out.println(queue);
}
}
}
}
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