学步园

思路详解参见：http://blog.sina.com.cn/s/blog_691ce2b70101lolv.html

这里用树状数组实现，时间要快很多。

//0 KB	113 ms
#include <stdio.h>
#include <string.h>
#define lowbit(x) (x &(-x))

const int M = 100005;
const int N = 20005;

int ar[M],val[N],lmin[N],rmin[N];

void add (int x)
{
    while (x <= M)
    ar[x] += 1,x += lowbit(x);
}
int sum(int x)
{
    int res  = 0;
    while (x > 0)
        res += ar[x],x -= lowbit(x);
    return res;
}
int main ()
{
    int T,n,i;
    scanf ("%d",&T);
    while (T--)
    {
        scanf ("%d",&n);
        memset (ar,0,sizeof(ar));
        for (i = 1;i <= n;i ++)
        {
            scanf ("%d",&val[i]);
            add(val[i]);
            lmin[i] = sum(val[i]-1);
        }
        memset (ar,0,sizeof(ar));
        for (i = n;i >= 1;i --)
        {
            add(val[i]);
            rmin[i] = sum(val[i]-1);
        }
        //for (i = 1;i <= n;i ++)
         //   printf ("%d %d\n",lmin[i],rmin[i]);
        long long ans = 0;
        for (i = 1;i <= n;i ++)
            ans += lmin[i]*(n-i-rmin[i])+(i-lmin[i]-1)*rmin[i];
        printf ("%lld\n",ans);
    }
    return 0;
}