c语言求逆序数代码

以下是一个使用归并排序求逆序数的 C 代码：

#include <stdio.h>

long long merge(int arr[], int temp[], int left, int mid, int right) {
    int i = left, j = mid, k = left;
    long long count = 0;
    while (i <= mid - 1 && j <= right) {
        if (arr[i] <= arr[j]) {
            temp[k++] = arr[i++];
        } else {
            temp[k++] = arr[j++];
            count += mid - i;
        }
    }
    while (i <= mid - 1) {
        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 (right > left) {
        int mid = (left + right) / 2;
        count += mergeSort(arr, temp, left, mid);
        count += mergeSort(arr, temp, mid + 1, right);
        count += merge(arr, temp, left, mid + 1, right);
    }
    return count;
}

int main() {
    int arr[] = { 1, 20, 6, 4, 5 };
    int n = sizeof(arr) / sizeof(arr[0]);
    int temp[n];
    long long count = mergeSort(arr, temp, 0, n - 1);
    printf("Number of inversions are %lld \n", count);
    return 0;
}