[codility]Array-inversion-count

// you can also use includes, for example:// #include <algorithm>long long getInversionCount(vector<int>& workArr, int start, int end){    if(start >= end) return 0;    int mid = start+(end-start)/2;    long long inversionCnt = getInversionCount(workArr, start, mid)                       + getInversionCount(workArr, mid+1, end);    //...count the inversion count between two part array, when sort them    vector<int> tmpArr(end-start+1);    int i = start;    int j = mid+1;    int k = 0;    while(i <= mid || j <= end)    {        if(i > mid) tmpArr[k++] = workArr[j++];        else if(j > end)        {            inversionCnt += j-mid-1;            tmpArr[k++] = workArr[i++];        }        else        {            if(workArr[i] <= workArr[j])//...= is very important here to make this algorithm right            {                inversionCnt += j-mid-1;                tmpArr[k++] = workArr[i++];            }            else tmpArr[k++] = workArr[j++];        }    }        for(k = 0; k < tmpArr.size(); ++k)        workArr[start+k] = tmpArr[k];    //...return result    return inversionCnt;    }int solution(const vector<int> &A) {    // write your code in C++98    //...using merge sort like methods to calculate the inversion count    vector<int> workArr = A;    long long ans = getInversionCount(workArr, 0, workArr.size()-1);    if(ans > 1000000000) return -1;    else return (int)ans;    }