5.模拟循环队列

为解决刚才队列的问题，引入循环队列来解决问题。

1.循环队列设计思路

• 预留一个空间作为约定，也就是说队列的最大容量变为了maxSize-1了
• front指针做tfron调整：front指向队中的头元素，初始值为front=0
• rear指针做调整：rear指向队列中最后一个元素的后一个元素，因为想空出一个空间作为元素，初始值为rear=0
• 队空判断条件：front==rear
• 队满判断条件：(rear+1)%maxSize == front
• 队中元素个数：(rear+maxSize-front)%maxSize

2.代码实现

package com.yc.day01.queue;

import java.util.Scanner;

public class LoopQueueTest {
    public static void main(String[] args) {
        LoopQueue queue = new LoopQueue(3);
        Scanner scanner = new Scanner(System.in);
        char key = ' ';
        boolean loop = true;
        while (loop){
            System.out.println("s(show):显示队列中所有元素");
            System.out.println("a(add):添加一个元素");
            System.out.println("p(pop):取出一个元素");
            System.out.println("g(getHead):获取头元素");
            System.out.println("l(length):获取队列长度");
            System.out.println("e(exit):退出");

            key = scanner.next().charAt(0);
            switch (key){
                case 's':
                    queue.print();
                    break;
                case 'a':
                    System.out.println("请输入一个数：");
                    int value = scanner.nextInt();
                    try{
                        queue.add(value);
                    }catch (Exception e){
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'p':
                    try{
                        int pop = queue.pop();
                        System.out.println("取出的元素为："+pop);
                    }catch (Exception e){
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'g':
                    try{
                        int head = queue.getHead();
                        System.out.println("头元素为："+head);
                    }catch (Exception e){
                        System.out.println(e.getMessage());
                    }
                    break;
                case 'l':
                    int length = queue.length();
                    System.out.println("队列元素个数为："+length);
                    break;
                case 'e':
                    loop = false;
                    scanner.close();
                    break;
                default:
                    break;
            }
        }
    }
}
class LoopQueue{
    private int maxSize;
    private int front;
    private int rear;
    private int[] arr;
    public LoopQueue(int maxSize){
        this.maxSize = maxSize;
        this.arr = new int[maxSize];
        this.front = 0;
        this.rear = 0;
    }
    public boolean isFull(){
        return (rear+1)%maxSize==front;
    }
    public boolean isEmpty(){
        return rear==front;
    }
    public void add(int i){
        if(isFull()){
            throw new RuntimeException("队列已满");
        }
        arr[rear] = i;
        rear = (rear+1)%maxSize;
    }
    public int pop(){
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        int value = arr[front];
        front = (front+1)%maxSize;
        return value;
    }
    public int getHead(){
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        return arr[front];
    }
    public int length(){
        return (rear+maxSize-front)%maxSize;
    }
    public void print(){
        for (int i = front; i < front+length(); i++) {
            System.out.printf("arr[%d]=%d\n",i%maxSize,arr[i%maxSize]);
        }
    }
}