题解 | #【模板】循环队列#

import java.util.*;

public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        solve01();
    }
    
/*
3 10
push 1
push 2
front
push 3
push 4
pop
pop
pop
front
pop

1
full
1
2
3
empty
empty
    */
    
/*
10 48
front
front
pop
push 6
front
push -3
push 14
pop
front
front
pop
front
pop
front
push -16
pop
pop
pop
push -9
front
front
front
push 11
front
pop
push 3
front
push 0
pop
pop
pop
push 0
push 4
push -15
push 9
front
pop
pop
front
pop
front
push -3
front
pop
front
front
front
pop

empty
empty
empty
6
6
-3
-3
-3
14
14
empty
-16
empty
empty
-9
-9
-9
-9
-9
11
11
3
0
0
0
4
-15
-15
9
9
9
-3
-3
-3
-3
*/
    static void solve01() {
        int n = sc.nextInt(), q = sc.nextInt();
        sc.nextLine();
        CirQueue queue = new CirQueue(n);
        while (q-- > 0) {
            String arr[] = sc.nextLine().split(" ");
            if (arr[0].equals("push")) {
                boolean flag = queue.push(Integer.parseInt(arr[1]));
                if (!flag) System.out.println("full");
            } else if (arr[0].equals("pop")) {
                Integer pop = (Integer) queue.pop();
                if (pop == null) {
                    System.out.println("empty");
                } else {
                    System.out.println(pop);
                }
            } else if (arr[0].equals("front")) {
                Integer top = (Integer) queue.front();
                if (top == null) {
                    System.out.println("empty");
                } else {
                    System.out.println(top);
                }
            }
        }
    }
}
/**
 * 循环队列
 */
class CirQueue {
    private int queueSize;
    private int front;
    private int rear;
    private Object queueList[];

    public CirQueue(int queueSize) {
        this.queueSize = queueSize + 1;
        queueList = new Object[this.queueSize];
        front = 0;
        rear = 0;
    }

    /**
     * 判断队列是否为空
     * @return
     */
    public boolean isEmpty() {
        return rear == front;
    }
    
    /**
     * 判断队列是否为满
     * @return
     */
    public boolean isFull() {
        return (rear + 1) % queueSize == front;
    }

    /**
     * 获取队列头元素
     * @return
     */
    public Object front() {
        // 如果队列不为空, 返回队头元素, 否则返回 null
        return isEmpty() ? null : queueList[front];
    }

    /**
     * 出队
     * @return
     */
    public Object pop() {
        if (isEmpty()) return null;
        Object ele = queueList[front];
        front = (front + 1) % queueSize;
        return ele;
    }

    /**
     * 入队
     * 如果队列未满, 添加元素到队尾, 否则提示队列已满
     * @param ele
     * @return
     */
    public boolean push(Object ele) {
        if (isFull()) return false;
        queueList[rear] = ele;
        rear = (rear + 1) % queueSize;
        return true;
    }
}