队列

package com.algorithms;

import java.util.Scanner;

/**
 * Created by Administrator on 2019/11/2 0002.
 */
public class CircleQueue {
    //定义一个数组
    private int[] arr;
    //数组的最大值
    private int maxSize;
    //头指针
    private int front;
    //尾指针
    private int tail;

    //创建一个带参的构造器，出入队列的大小
    public CircleQueue(int maxSize){
        this.maxSize = maxSize;
        arr = new int[maxSize];
    }

    //数据测试
    public static void main(String[] args) {
        CircleQueue circleQueue = new CircleQueue(5);
        System.out.println("根据提示输入相关值");
        Scanner in = new Scanner(System.in);
        while (true){
            System.out.println("s:显示");
            System.out.println("o:输入");
            System.out.println("p:输出");
            System.out.println("h:头出");
            String next = in.next();
            switch (next){
                case "s" : circleQueue.list(); break;
                case "o" :
                    System.out.println("请输入一个数");
                    int i = in.nextInt();
                    circleQueue.offer(i);
                    break;
                case "p" :
                    int poll = circleQueue.poll();
                    System.out.println(poll);
                    break;
                case "h" :
                    int peek = circleQueue.peek();
                    System.out.println(peek);
                    break;
            }
        }
    }

    //判断队列是否已满，根据我们的约定来,虽然它还能存放一个元素。
    //这里面没几个难点。。。这算一个**********************
    public boolean isFull(){
        return (tail + 1) % maxSize == front;
    }
    //插入方法
    public void offer(int num){
        if(isFull()){
            throw  new RuntimeException("队列已满");
        }
        arr[tail]=num;
        //不能直接 ++ 否则可以数据越界
        //这里面没几个难点。。。这算一个**********************
        tail = (tail + 1) % maxSize;
    }

    //判断队列是否为空
    public boolean isEmpty(){
        return tail == front;
    }

    public int poll(){
        if(isEmpty()){
            throw new RuntimeException("队列为空");
        }
        int temp = arr[front];
        //不能直接 ++ 否则可以数据越界
        front = (front + 1) % maxSize;
        return temp;
    }

    //查看队列的大小
    public int size(){
        //tail+maxSize 是防止队列存满后，tail=2 在 front=3 的前面这种为负数的情况
        // %maxSize 是防止计算的结果大于 maxSize
        //这里面没几个难点。。。这算一个**********************
        return (tail+maxSize-front)%maxSize;
    }

    //循环查看所有元素信息
    public void list(){
        for(int i = front;i< front + size();i++){
            System.out.printf("arr[%d]==%d\n",i%maxSize,arr[i%maxSize]);
        }
    }

    //查看栈顶元素
    public int peek(){
        return arr[front];
    }
}



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