cpp-algo-cases/chapter_stack_and_queue/array_deque.cpp

/**
 * File: array_deque.cpp
 * Created Time: 2023-03-02
 * Author: krahets (krahets@163.com)
 */

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

/* 基于环形数组实现的双向队列 */
class ArrayDeque
{
private:
    vector<int> nums; // 用于存储双向队列元素的数组
    int front;        // 队首指针，指向队首元素
    int queSize;      // 双向队列长度

public:
    /* 构造方法 */
    ArrayDeque(int capacity)
    {
        nums.resize(capacity);
        front = queSize = 0;
    }

    /* 获取双向队列的容量 */
    int capacity()
    {
        return nums.size();
    }

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

    /* 判断双向队列是否为空 */
    bool isEmpty()
    {
        return queSize == 0;
    }

    /* 计算环形数组索引 */
    int index(int i)
    {
        // 通过取余操作实现数组首尾相连
        // 当 i 越过数组尾部后，回到头部
        // 当 i 越过数组头部后，回到尾部
        return (i + capacity()) % capacity(); // 保证返回值在 [0, capacity) 范围内
    }

    /* 队首入队 */
    void pushFirst(int num)
    {
        if (queSize == capacity())
        {
            cout << "双向队列已满" << endl;
            return;
        }
        // 队首指针向左移动一位
        // 通过取余操作实现 front 越过数组头部后回到尾部
        front = index(front - 1);
        // 将 num 添加至队首
        nums[front] = num;
        queSize++;
    }

    /* 队尾入队 */
    void pushLast(int num)
    {
        if (queSize == capacity())
        {
            cout << "双向队列已满" << endl;
            return;
        }
        // 计算队尾指针，指向队尾索引 + 1
        int rear = index(front + queSize);
        // 将 num 添加至队尾
        nums[rear] = num;
        queSize++;
    }

    /* 队首出队 */
    int popFirst()
    {
        int num = peekFirst();
        // 队首指针向后移动一位
        front = index(front + 1); // 移动 front 指针的目的是为了使得队首元素不再属于队列
        queSize--;
        return num;
    }

    /* 队尾出队 */
    int popLast()
    {
        int num = peekLast();
        queSize--;
        return num;
    }

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

    /* 访问队尾元素 */
    int peekLast()
    {
        if (isEmpty())
            throw out_of_range("双向队列为空");
        // 计算尾元素索引
        int last = index(front + queSize - 1); // 通过 front 和 queSize 计算出队尾元素索引
        return nums[last];
    }

    /* 返回数组用于打印 */
    vector<int> toVector()
    {
        // 仅转换有效长度范围内的列表元素
        vector<int> res(queSize);
        for (int i = 0, j = front; i < queSize; i++, j++)
        {
            res[i] = nums[index(j)];
        }
        return res;
    }
};

/* Driver Code */
int main()
{
    /* 初始化双向队列 */
    ArrayDeque *deque = new ArrayDeque(10);
    deque->pushLast(3);
    deque->pushLast(2);
    deque->pushLast(5);
    cout << "双向队列 deque = ";
    printVector(deque->toVector());

    /* 访问元素 */
    int peekFirst = deque->peekFirst();
    cout << "队首元素 peekFirst = " << peekFirst << endl;
    int peekLast = deque->peekLast();
    cout << "队尾元素 peekLast = " << peekLast << endl;

    /* 元素入队 */
    deque->pushLast(4);
    cout << "元素 4 队尾入队后 deque = ";
    printVector(deque->toVector());
    deque->pushFirst(1);
    cout << "元素 1 队首入队后 deque = ";
    printVector(deque->toVector());

    /* 元素出队 */
    int popLast = deque->popLast();
    cout << "队尾出队元素 = " << popLast << "，队尾出队后 deque = ";
    printVector(deque->toVector());
    int popFirst = deque->popFirst();
    cout << "队首出队元素 = " << popFirst << "，队首出队后 deque = ";
    printVector(deque->toVector());

    /* 获取双向队列的长度 */
    int size = deque->size();
    cout << "双向队列长度 size = " << size << endl;

    /* 判断双向队列是否为空 */
    bool isEmpty = deque->isEmpty();
    cout << "双向队列是否为空 = " << boolalpha << isEmpty << endl;
    return 0;
}