HDU 2838 Cow Sorting

#include<bits/stdc++.h>
using namespace std;
#define N 100005
#define ll long long int
int a[N],cnt[N],n,k,t;
ll sum[N],ans;

int lowbit(int x)
{
    return x&(-x);
}

void add(int x)
{
    int d=x;
    while(x<=n)
    {
        cnt[x]++;
        sum[x]+=d;
        x+=lowbit(x);
    }
}

int sum1(int x)
{
    int s=0;
    while(x)
    {
        s+=cnt[x];
        x-=lowbit(x);
    }
    return s;
}

ll sum2(int x)
{
    ll s=0;
    while(x)
    {
        s+=sum[x];
        x-=lowbit(x);
    }
    return s;
}

int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
        add(a[i]);
        t=sum1(a[i]);
        k=i-t;
        if(k!=0)
        {
            ans+=(ll)a[i]*k;
            ans+=sum2(n)-sum2(a[i]);
        }
    }
    printf("%I64d\n",ans);
    return 0;
}