Hdu 2492 树状数组 Ping pong

#include<iostream>
#include<cstdio>
#include<cstring>
#define MAXN 100005
#define M 20005
typedef __int64 LL ;
using namespace std;
LL n,max_num ;
LL s[M],a[M],b[M],c[MAXN];
LL lowbit(LL x){
    return x&(-x);
}
LL sum(LL x){
    LL ret = 0;
    while(x > 0){
        ret += c[x];
        x -= lowbit(x);
    }
    return ret;
}
void add(LL x, LL d){
    while(x<=max_num){
        c[x] += d;
        x += lowbit(x);
    }
}
int main(){
    LL t,i,j,ans;
    cin>>t;
    while(t--){
        cin>>n;
        max_num = 0;
        for(i = 1;i <= n ;i++){
            scanf("%I64d",&s[i]);
            if(s[i]>max_num)
                max_num = s[i];
        }
        memset(c,0,sizeof(c));
        for(i = 1;i <= n ; i++){
            add(s[i],1);
            a[i] = sum(s[i]-1);
        }
        memset(c,0,sizeof(c));
        for(i = n; i>0 ;i--){
            add(s[i],1);
            b[i] = sum(s[i]-1);
        }
        ans = 0;
        for(i = 1;i <= n ;i++){
            //cout<<a[i]<<" "<<b[i]<<endl;
            ans = ans+a[i]*(n-i-b[i])+(i-a[i]-1)*b[i];
        }
        cout<<ans<<endl;
    }
    return 0;
}