Code/INVCNT.cpp at master · sushiljacksparrow/Code · GitHub

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#include<iostream>
#include<string>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<stack>
#include<cctype>
#include<cmath>
#include<cstring>
#include<queue>
#include<cstdio>
#include<sstream>
using namespace std;
#define pb push_back
#define pi 3.141592653589793238462643383
long long merge(int a[],int l,int mid,int h,int temp[]){
    int i,j,k;

    long long count=0;
    j = mid+1;
    for(k=l;k<=mid;k++){
        while(j<=h){
            if(a[k]>a[j])
                j++;
            else
                break;
        }
        count+=j-(mid+1);
    }

    i = l;
    j = mid+1;
    k = l;
    while(i<=mid&&j<=h){
        if(a[i]<a[j]){
            temp[k] = a[i];
            i++;k++;
        }
        else
        {
            temp[k] = a[j];
            j++;
            k++;
        }
    }
    while(i<=mid){
        temp[k] = a[i];
        i++;k++;
    }
    while(j<=h){
        temp[k] =  a[j];
        j++;k++;
    }
    for(k=l;k<=h;k++)
        a[k] = temp[k];
    return count;
}
long long mergesort(int a[],int l,int h,int temp[]){
    if(l==h)
        return 0;
    int mid;
    mid = (l+h)/2;
    long long lc,rc,mc;
    lc = mergesort(a,l,mid,temp);
    rc = mergesort(a,mid+1,h,temp);
    mc = merge(a,l,mid,h,temp);
    return lc+rc+mc;
}
int main()
{
    int t,n,i,j;
    scanf("%d",&t);
    while(t>0){
        scanf("%d",&n);
        int a[n],temp[n];
        for(i=0;i<n;i++)
            scanf("%d",&a[i]);
        long long ans = mergesort(a,0,n-1,temp);
        printf("%lld\n",ans);
        t--;
    }
}