循环队列

Posted 2021-03-11 hetaoyuan

 

假设循环队列最多能容纳k个整型数字，那么我们需要开辟k+1个空间，如图，当k = 6的时候，空间大小为7，即array.length() = 7.在起始的时候，front = rear = 0；在每次添加数字的时候( enqueue() ),rear都会+1，而k = 6，也就是从初始位置rear = 0时，最多一直连续添加6次，此时 rear = 6,无法再次添加，那么要想再次添加，只有通过出队列(dequeue()),每出一次队列，front的值都会+1，最多加到front = 6，此时，队列为空，那么rear和front的值都为6，再次入队列，rear会重新从0开始计算，再次出队列，front也会从0开始计算。每次删除的时候，从(front+1)/array.lenth()的位置删，每次添加的时候从(rear+1)/array.length()的位置添加.

 

 

 

class MyCircularQueue {

    private int front;//队列头
    private int rear;//队列尾
    private int usedSize;//数据个数
    private int[] elem;//数组


    /** Initialize your data structure here.
     * Set the size of the queue to be k. */
    public MyCircularQueue(int k) {
        this.elem = new int[k+1];
        this.front = 0;
        this.rear = 0;
        this.usedSize = 0;
    }

    /** Insert an element into the circular queue.
     * Return true if the operation is successful. */
    public boolean enQueue(int value) {
        if(isFull()){
            return false;
        }
        this.elem[this.rear] = value;
        this.rear = (this.rear+1)%this.elem.length;
        this.usedSize++;
        return true;
    }

    /** Delete an element from the circular queue.
     * Return true if the operation is successful. */
    public boolean deQueue() {
        if(isEmpty()){
            return false;
        }
        this.front = (this.front+1)%this.elem.length;
        this.usedSize--;
        return true;
    }

    /** Get the front item from the queue. */
    public int Front() {
        if(isEmpty()){
            return -1;
        }
        return this.elem[this.front];
    }

    /** Get the last item from the queue. */
    public int Rear() {
        if(isEmpty()){
            return -1;
        }
        int index = this.rear == 0 ? this.elem.length-1 : this.rear-1;
        return this.elem[index];
    }

    /** Checks whether the circular queue is empty or not. */
    public boolean isEmpty() {
        return this.rear == this.front;
    }

    /** Checks whether the circular queue is full or not. */
    public boolean isFull() {
        if((this.rear+1)%this.elem.length == this.front){
            return true;
        }
        return false;
    }
}

class Main1{
    public static void main(String[] args) {
       MyCircularQueue myCircularQueue = new MyCircularQueue(6);
        for (int i = 1; i <=10; i++) {
            myCircularQueue.enQueue(i);
        }
        for (int i = 1; i <= 4; i++) {
            myCircularQueue.deQueue();
        }
        for (int i = 1; i <= 3; i++) {
            myCircularQueue.enQueue(i);
        }
        for (int i = 1; i <=3 ; i++) {
            myCircularQueue.deQueue();
        }
        for (int i = 1; i <=3 ; i++) {
            myCircularQueue.enQueue(i);
        }
        System.out.println(myCircularQueue.Front());
    }
}