c++归并排序逆序对

以下是C++中使用归并排序求逆序对的代码示例：

#include <iostream>
using namespace std;

long long merge(int arr[], int temp[], int left, int mid, int right) {
    int i = left; // 左子数组的起始下标
    int j = mid + 1; // 右子数组的起始下标
    int k = left; // 合并后数组的起始下标
    long long count = 0; // 逆序对的数量

    while (i <= mid && j <= right) {
        if (arr[i] <= arr[j]) {
            temp[k++] = arr[i++];
        } else {
            temp[k++] = arr[j++];
            count += (mid - i + 1); // 统计逆序对数量
        }
    }

    while (i <= mid) {
        temp[k++] = arr[i++];
    }

    while (j <= right) {
        temp[k++] = arr[j++];
    }

    for (i = left; i <= right; i++) {
        arr[i] = temp[i];
    }

    return count;
}

long long mergeSort(int arr[], int temp[], int left, int right) {
    long long count = 0;

    if (left < right) {
        int mid = (left + right) / 2;
        count += mergeSort(arr, temp, left, mid);
        count += mergeSort(arr, temp, mid + 1, right);
        count += merge(arr, temp, left, mid, right);
    }

    return count;
}

long long getInversePairs(int arr[], int n) {
    int *temp = new int[n];
    long long count = mergeSort(arr, temp, 0, n - 1);
    delete[] temp;
    return count;
}

int main() {
    int arr[] = { 7, 5, 6, 4 };
    int n = sizeof(arr) / sizeof(arr[0]);
    long long count = getInversePairs(arr, n);
    cout << "逆序对的数量为：" << count << endl;
    return 0;
}