实现合并排序算法。要排序的整型数组元素可以用随机数生成器生成，运行程序，分别记录对十万，一百万，一千万，五千万个数据排序所用的时间，列出表格显示统计出来的时间。并单独显示一个100个数据的排序结果。使用c++编写

好的，以下是用 C++ 实现的合并排序算法程序，满足您的要求：

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <chrono>

using namespace std;

void merge(int arr[], int l, int m, int r) {
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;

    int L[n1], R[n2];

    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1 + j];

    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        }
        else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }

    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(int arr[], int l, int r) {
    if (l < r) {
        int m = l + (r - l) / 2;

        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);

        merge(arr, l, m, r);
    }
}

void printArray(int arr[], int size) {
    int i;
    for (i = 0; i < size; i++)
        cout << arr[i] << " ";
    cout << endl;
}

int main() {
    int i, n;
    double time_used;

    // 10^5
    n = 100000;
    int arr1[n];
    for (i = 0; i < n; i++)
        arr1[i] = rand();
    auto start1 = chrono::high_resolution_clock::now();
    mergeSort(arr1, 0, n - 1);
    auto end1 = chrono::high_resolution_clock::now();
    time_used = chrono::duration_cast<chrono::microseconds>(end1 - start1).count() / 1e6;
    cout << "Time taken for " << n << " elements: " << time_used << " seconds" << endl;

    // 10^6
    n = 1000000;
    int arr2[n];
    for (i = 0; i < n; i++)
        arr2[i] = rand();
    auto start2 = chrono::high_resolution_clock::now();
    mergeSort(arr2, 0, n - 1);
    auto end2 = chrono::high_resolution_clock::now();
    time_used = chrono::duration_cast<chrono::microseconds>(end2 - start2).count() / 1e6;
    cout << "Time taken for " << n << " elements: " << time_used << " seconds" << endl;

    // 10^7
    n = 10000000;
    int arr3[n];
    for (i = 0; i < n; i++)
        arr3[i] = rand();
    auto start3 = chrono::high_resolution_clock::now();
    mergeSort(arr3, 0, n - 1);
    auto end3 = chrono::high_resolution_clock::now();
    time_used = chrono::duration_cast<chrono::microseconds>(end3 - start3).count() / 1e6;
    cout << "Time taken for " << n << " elements: " << time_used << " seconds" << endl;

    // 5*10^7
    n = 50000000;
    int arr4[n];
    for (i = 0; i < n; i++)
        arr4[i] = rand();
    auto start4 = chrono::high_resolution_clock::now();
    mergeSort(arr4, 0, n - 1);
    auto end4 = chrono::high_resolution_clock::now();
    time_used = chrono::duration_cast<chrono::microseconds>(end4 - start4).count() / 1e6;
    cout << "Time taken for " << n << " elements: " << time_used << " seconds" << endl;

    // print sorted array of 100 elements
    n = 100;
    int arr5[n];
    for (i = 0; i < n; i++)
        arr5[i] = rand();
    cout << "Before sorting:" << endl;
    printArray(arr5, n);
    mergeSort(arr5, 0, n - 1);
    cout << "After sorting:" << endl;
    printArray(arr5, n);

    return 0;
}

这个程序与之前的 C 语言程序相似，但使用了 C++ 的库函数 `chrono` 来计时。它同样通过 `mergeSort` 函数实现了合并排序算法，并输出了对于四个不同规模的数组所用的时间。最后，它还输出了一个由随机生成的100个元素组成的数组的排序结果。

注意：这个程序只是演示了如何使用合并排序算法，实际应用中可能需要考虑更多因素，如算法的稳定性、内存占用等。