队列介绍
1)队列是一个有序列表，可以用数组或是链表来实现。
2)遵循先入先出的原则。即:先存入队列的数据，要先取出。后存入的要后取出
实现队列
数组模拟队列
package edu.cqupt._02队列;
/**
* @description 数组模拟队列
* @author lin.z
* @Date 2020/08/28
*/
public class ArrayQueue {
private int maxSize;
private int front;
private int rear;
private int[] arr;
public ArrayQueue(int maxSize) {
this.maxSize = maxSize;
front = -1;
rear = -1;
arr = new int[maxSize];
}
/**
* @description 判断队列是否满
* @return boolean
*/
public boolean isFull(){
return rear == maxSize - 1;
}
/**
* @description 判断队列是否为空
* @return：boolean
*/
public boolean isEmpty(){
return front == rear;
}
/**
* @description 入队列
* @param element
*/
public void push(int element){
if(isFull()){
System.out.println("队列满，不能插入数据。");
return;
}else{
arr[++rear] = element;
}
}
/**
* @description 出队列
* @return
*/
public int pop(){
if(isEmpty()){
throw new RuntimeException("队列为空，不能取出数据。");
}else{
return arr[++front];
}
}
/**
* @description 显示队列头元素(此处不是取出,front不能变化)
* @return
*/
public int head(){
if(isEmpty()){
throw new RuntimeException("队列为空，没有头元素。");
}else{
return arr[front+1];
}
}
public void show(){
if(isEmpty()){
throw new RuntimeException("队列为空，没有头元素。");
}else{
for (int i = 0; i <arr.length ; i++) {
System.out.printf("arr[%d] = %d ", i,arr[i]);
}
System.out.println();
}
}
}
测试类
package edu.cqupt._02队列;
import java.util.Scanner;
public class DemoApp {
public static void main(String[] args) {
ArrayQueue queue = new ArrayQueue(3);
char key = ' ';
Scanner scanner = new Scanner(System.in);
boolean flag = true;
System.out.println("s(show),显示队列");
System.out.println("e(exit),退出程序");
System.out.println("a(push),添加元素");
System.out.println("g(pop),取出元素");
System.out.println("h(head),显示队列头元素");
while (flag){
System.out.println("-------------");
key = scanner.next().charAt(0); // 接收一个字符
switch (key){
case 'a':
System.out.println("请输入一个数:");
int element = scanner.nextInt();
queue.push(element);
break;
case 'g':
int res = queue.pop();
System.out.println("取出的数据为：" + res);
break;
case 'h':
int h = queue.head();
System.out.println("队列头元素为：" + h);
break;
case 's':
System.out.println("队列中的数据为:");
queue.show();
break;
case 'e':
scanner.close();
flag = false;
break;
default:
break;
}
}
}
}
- 测试结果
数组模拟环形队列
对前面的数组模拟队列的优化，充分利用数组.因此将数组看做是一个环形的。(通过取模的方式来实现即可)
- 队列为空的情况
队列为空：front == rear;
- 入队列及队列长度
入队列：arr[rear] = element; rear =(rear+1)% maxSize;
队列长度：(rear + maxSize - front) % maxSize;
- 出队列以及队列为满的情况
出队列：int value = arr[front]; front = (front+1) % maxSize;返回value，value即为取出的元素
队列为满：(rear + 1) % maxSize == front
package edu.cqupt._02队列;
/**
* @description 数组模拟循环队列
* @author lin.z
* @Date 2020/08/31
*/
public class CircleQueue {
private int maxSize;
private int front;
private int rear;
private int[] arr;
public CircleQueue(int maxSize) {
this.maxSize = maxSize;
front = 0;
rear = 0;
arr = new int[maxSize];
}
/**
* @description：判断队列是否满
* @return：boolean
*/
public boolean isFull(){
return (rear+1) % maxSize == front;
}
/**
* @description：判断队列是否为空
* @return：boolean
*/
public boolean isEmpty(){
return front == rear;
}
/**
* @description：入队列
* @param：element
*/
public void push(int element){
if(isFull()){
System.out.println("队列满，不能插入数据。");
return;
}else{
arr[rear] = element;
rear = (rear+1)% maxSize;
}
}
/**
* @description：出队列
* @return：int
*/
public int pop(){
if(isEmpty()){
throw new RuntimeException("队列为空，不能取出数据。");
}else{
int value = arr[front];
front = (front + 1) % maxSize;
return value;
}
}
/**
* @description：显示队列头元素(此处不是取出,front不能变化)
* @return：int
*/
public int head(){
if(isEmpty()){
throw new RuntimeException("队列为空，没有头元素。");
}else{
return arr[front];
}
}
/**
* @description:队列中的元素个数
* @return:int
*/
public int length(){
return (rear + maxSize - front) % maxSize;
}
public void show(){
if(isEmpty()){
throw new RuntimeException("队列为空，没有头元素。");
}else{
for (int i = 0; i <arr.length ; i++) {
System.out.printf("arr[%d] = %d ", i%maxSize,arr[i%maxSize]);
}
System.out.println();
}
}
}
测试类
package edu.cqupt._02队列;
import java.util.Scanner;
public class DemoApp2 {
public static void main(String[] args) {
CircleQueue queue = new CircleQueue(3);
char key = ' ';
Scanner scanner = new Scanner(System.in);
boolean flag = true;
System.out.println("s(show),显示队列");
System.out.println("e(exit),退出程序");
System.out.println("a(push),添加元素");
System.out.println("g(pop),取出元素");
System.out.println("l(pop),队列求长度");
System.out.println("h(head),显示队列头元素");
while (flag){
System.out.println("-------------");
key = scanner.next().charAt(0); // 接收一个字符
switch (key){
case 'a':
System.out.println("请输入一个数:");
int element = scanner.nextInt();
queue.push(element);
break;
case 'g':
int res = queue.pop();
System.out.println("取出的数据为：" + res);
break;
case 'h':
int h = queue.head();
System.out.println("队列头元素为：" + h);
break;
case 'l':
int len = queue.length();
System.out.println("队列长度为：" + len);
break;
case 's':
System.out.println("队列中的数据为:");
queue.show();
break;
case 'e':
scanner.close();
flag = false;
break;
default:
break;
}
}
}
}
- 测试结果
