编辑代码

#include <stdio.h>

int merge(int arr[], int temp[], int left, int mid, int right) {
    int i = left;
    int j = mid + 1;
    int k = left;
    int count = 0;

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

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

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

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

    return count;
}

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);
        count += merge(arr, temp, left, mid, right);
    }

    return count;
}

int main() {
    int arr[] = {2, 4, 3, 1, 5, 6};
    int n = sizeof(arr) / sizeof(arr[0]);
    int temp[n];

    int count = mergeSort(arr, temp, 0, n - 1);

    printf("逆序对个数：%d\n", count);

    return 0;
}