1013 逆序对

#include<iostream>
using namespace std;

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

    i = left; /* i is index for left subarray*/
    j = mid; /* j is index for right subarray*/
    k = left; /* k is index for resultant merged subarray*/
    while ((i <= mid - 1) && (j <= right)) {
        if (arr[i] <= arr[j]) {
            temp[k++] = arr[i++];
        }
        else {
            temp[k++] = arr[j++];

            inv_count = inv_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 inv_count;
}

int _mergeSort(int arr[], int temp[], int left, int right)
{
    int inv_count = 0;
    if (right > left) {
        int mid = (right + left) / 2;

        inv_count += _mergeSort(arr, temp, left, mid);
        inv_count += _mergeSort(arr, temp, mid + 1, right);

        inv_count += merge(arr, temp, left, mid + 1, right);
    }
    return inv_count;
}

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

int main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        int size;
        cin>>size;
        int arr[size];
        for(int j=0;j<size;j++)
        {
            cin>>arr[j];
        }
        cout<<mergeSort(arr, size)<<endl;
    }
    return 0;
}