hello-algo/codes/cpp/chapter_stack_and_queue/array_queue.cpp

/**
 * File: array_queue.cpp
 * Created Time: 2022-11-25
 * Author: Krahets (krahets@163.com)
 */

#include "../utils/common.hpp"

/* 基于环形数组实现的队列 */
class ArrayQueue {
  private:
    int *nums;       // 用于存储队列元素的数组
    int front;       // 队首指针，指向队首元素
    int queSize;     // 队列长度
    int queCapacity; // 队列容量

  public:
    ArrayQueue(int capacity) {
        // 初始化数组
        nums = new int[capacity];
        queCapacity = capacity;
        front = queSize = 0;
    }

    ~ArrayQueue() {
        delete[] nums;
    }

    /* 获取队列的容量 */
    int capacity() {
        return queCapacity;
    }

    /* 获取队列的长度 */
    int size() {
        return queSize;
    }

    /* 判断队列是否为空 */
    bool isEmpty() {
        return size() == 0;
    }

    /* 入队 */
    void push(int num) {
        if (queSize == queCapacity) {
            cout << "队列已满" << endl;
            return;
        }
        // 计算队尾指针，指向队尾索引 + 1
        // 通过取余操作，实现 rear 越过数组尾部后回到头部
        int rear = (front + queSize) % queCapacity;
        // 将 num 添加至队尾
        nums[rear] = num;
        queSize++;
    }

    /* 出队 */
    void pop() {
        int num = peek();
        // 队首指针向后移动一位，若越过尾部则返回到数组头部
        front = (front + 1) % queCapacity;
        queSize--;
    }

    /* 访问队首元素 */
    int peek() {
        if (isEmpty())
            throw out_of_range("队列为空");
        return nums[front];
    }

    /* 将数组转化为 Vector 并返回 */
    vector<int> toVector() {
        // 仅转换有效长度范围内的列表元素
        vector<int> arr(queSize);
        for (int i = 0, j = front; i < queSize; i++, j++) {
            arr[i] = nums[j % queCapacity];
        }
        return arr;
    }
};

/* Driver Code */
int main() {
    /* 初始化队列 */
    int capacity = 10;
    ArrayQueue *queue = new ArrayQueue(capacity);

    /* 元素入队 */
    queue->push(1);
    queue->push(3);
    queue->push(2);
    queue->push(5);
    queue->push(4);
    cout << "队列 queue = ";
    printVector(queue->toVector());

    /* 访问队首元素 */
    int peek = queue->peek();
    cout << "队首元素 peek = " << peek << endl;

    /* 元素出队 */
    queue->pop();
    cout << "出队元素 pop = " << peek << "，出队后 queue = ";
    printVector(queue->toVector());

    /* 获取队列的长度 */
    int size = queue->size();
    cout << "队列长度 size = " << size << endl;

    /* 判断队列是否为空 */
    bool empty = queue->isEmpty();
    cout << "队列是否为空 = " << empty << endl;

    /* 测试环形数组 */
    for (int i = 0; i < 10; i++) {
        queue->push(i);
        queue->pop();
        cout << "第 " << i << " 轮入队 + 出队后 queue = ";
        printVector(queue->toVector());
    }

    // 释放内存
    delete queue;

    return 0;
}