实现归并排序的openmp程序

以下是使用OpenMP实现归并排序的示例程序：

#include <iostream>
#include <omp.h>

void merge(double* a, double* b, int start, int mid, int end) {
    int i = start, j = mid + 1, k = start;
    while (i <= mid && j <= end) {
        if (a[i] <= a[j]) {
            b[k++] = a[i++];
        } else {
            b[k++] = a[j++];
        }
    }
    while (i <= mid) {
        b[k++] = a[i++];
    }
    while (j <= end) {
        b[k++] = a[j++];
    }
    for (int i = start; i <= end; i++) {
        a[i] = b[i];
    }
}

void mergeSort(double* a, double* b, int start, int end) {
    if (start < end) {
        int mid = (start + end) / 2;
        #pragma omp parallel sections
        {
            #pragma omp section
            {
                mergeSort(a, b, start, mid);
            }
            #pragma omp section
            {
                mergeSort(a, b, mid + 1, end);
            }
        }
        merge(a, b, start, mid, end);
    }
}

int main() {
    int n = 10; // 数组大小
    int p = 4; // 线程数

    double* a = new double[n];
    double* b = new double[n];

    // 初始化数组a和b
    #pragma omp parallel for
    for (int i = 0; i < n; i++) {
        a[i] = rand() / double(RAND_MAX);
        b[i] = 0;
    }

    // 排序数组a和b
    double start_time = omp_get_wtime();
    mergeSort(a, b, 0, n - 1);
    double end_time = omp_get_wtime();

    // 检测归并结果是否正确
    bool isSorted = true;
    for (int i = 1; i < n; i++) {
        if (a[i] < a[i - 1]) {
            isSorted = false;
            break;
        }
    }

    // 输出排序结果和归并时间
    if (isSorted) {
        std::cout << "归并排序结果：";
        for (int i = 0; i < n; i++) {
            std::cout << a[i] << " ";
        }
        std::cout << std::endl;
    } else {
        std::cout << "归并排序结果不正确！" << std::endl;
    }
    std::cout << "归并时间：" << end_time - start_time << "秒" << std::endl;

    delete[] a;
    delete[] b;

    return 0;
}