用C（gcc）写

好的，下面是用C语言实现统计逆序对的代码：

#include <stdio.h>

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

int countInversions(int arr[], int n) {
    int temp[n];
    return mergeSort(arr, temp, 0, n - 1);
}

int main() {
    int arr[] = {1, 3, 2, 4, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    int count = countInversions(arr, n);
    printf("Number of inversions: %d\n", count);
    return 0;
}

这个代码和之前的Python代码思路是一样的，使用归并排序的思想，在归并排序的过程中统计逆序对的个数。该代码的时间复杂度为O(nlogn)。