B3616

cpp
#include <iostream>

class Queue {
private:
    int* data;
    int front;
    int rear;
    int capacity;
    int size;

public:
    Queue(int cap) {
        data = new int[cap];
        capacity = cap;
        front = rear = -1;
        size = 0;
    }

    ~Queue() {
        delete[] data;
    }

    void push(int x) {
        if (size == capacity) {
            std::cout << "ERR_CANNOT_PUSH" << std::endl;
        } else {
            rear = (rear + 1) % capacity;
            data[rear] = x;
            if (size == 0) {
                front = rear;
            }
            size++;
        }
    }

    void pop() {
        if (size == 0) {
            std::cout << "ERR_CANNOT_POP" << std::endl;
        } else {
            front = (front + 1) % capacity;
            size--;
        }
    }

    void query() {
        if (size == 0) {
            std::cout << "ERR_CANNOT_QUERY" << std::endl;
        } else {
            std::cout << data[front] << std::endl;
        }
    }

    int getSize() {
        return size;
    }
};

int main() {
    int n;
    std::cin >> n;

    Queue q(100); // 假设队列最大容量为100

    for (int i = 0; i < n; i++) {
        int op;
        std::cin >> op;
        if (op == 1) {
            int x;
            std::cin >> x;
            q.push(x);
        } else if (op == 2) {
            q.pop();
        } else if (op == 3) {
            q.query();
        } else if (op == 4) {
            std::cout << q.getSize() << std::endl;
        }
    }

    return 0;
}