数组实现循环队列

循环队列：

1. 需要预留一个空间，即rear指向的空间，否则无法判断队列为空或者为满
2. 空队列条件：rear == front
3. 满队列条件：( rear + 1 ) % maxSize = front

public class CircleArrayQueue {

    private int maxSize;
    private int[] queue;
    private int front;  //队首
    private int rear;   //队尾
    /* 说明:
        1、为什么环形队列需要预留一个空间：如果不预留，当 front=rear 时不能判断为空还是队满
        2、将 front 和 rear 的初始值都设为0，且 rear 永远指向最后一个元素的后一个位置。浪费的空间是rear所在位置
     */
    public CircleArrayQueue(int maxSize){
        this.maxSize = maxSize;
        this.queue = new int[maxSize];
    }

    public boolean isFull(){
        return (rear+1) % maxSize == front;
    }

    public boolean isEmpty(){
        return rear==front;
    }

    // 入队
    public void add(int value){
        if(isFull()){
            System.out.println("环形队列已满");
            return;
        }
        queue[rear] = value;
        rear = (rear + 1) % maxSize;
    }

    // 出队
    public int get(){
        if(isEmpty()){
            throw new RuntimeException("环形队列为空");
        }
        int value = queue[front];
        front = (front + 1) % maxSize;
        return value;
    }

    // 队列大小
    public int size(){
        return (rear + maxSize - front) % maxSize;
    }

    // 查看队首，不出队
    public int head(){
        if(isEmpty()){
            throw new RuntimeException("环形队列为空");
        }
        return queue[front];
    }

    // 遍历队列
    public void show(){
        if(isEmpty()){
            throw new RuntimeException("环形队列为空");
        }
        for(int i = front; i < front+size(); i++){
            System.out.printf("arr[%d]=%d\n", i % maxSize, queue[i % maxSize]);
        }
    }
}

测试代码：

public class Test {

    public static void main(String[] args){
         // 环形队列
        CircleArrayQueue circleArrayQueue = new CircleArrayQueue(3);
        circleArrayQueue.add(1);
        System.out.println("size:"+circleArrayQueue.size());
        circleArrayQueue.add(2);
        System.out.println("size:"+circleArrayQueue.size());
        circleArrayQueue.get();
        System.out.println("size:"+circleArrayQueue.size());
        circleArrayQueue.add(3);
        System.out.println("size:"+circleArrayQueue.size());
        circleArrayQueue.show();
    }
}