# HDU 5496(Beauty of Sequence-DP)

```#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<functional>
#include<iostream>
#include<map>
#include<cmath>
#include<cctype>
#include<ctime>
using namespace std;
#define For(i,n) for(int i=1;i<=n;i++)
#define Fork(i,k,n) for(int i=k;i<=n;i++)
#define Rep(i,n) for(int i=0;i<n;i++)
#define ForD(i,n) for(int i=n;i;i--)
#define RepD(i,n) for(int i=n;i>=0;i--)
#define Forp(x) for(int p=pre[x];p;p=next[p])
#define Forpiter(x) for(int &p=iter[x];p;p=next[p])
#define Lson (x<<1)
#define Rson ((x<<1)+1)
#define MEM(a) memset(a,0,sizeof(a));
#define MEMI(a) memset(a,127,sizeof(a));
#define MEMi(a) memset(a,128,sizeof(a));
#define INF (2139062143)
#define F (1000000007LL)
#define mp make_pair
#define fi first
#define se second
#define MAXN (100000+10)
typedef __int64 ll;
int n;
ll a[MAXN];
ll pow2(ll a,ll b)
{
ll c=1;
static bool a2[MAXN];
int n=0;while (b) a2[++n]=b&1,b>>=1;
For(i,n)
{
if (a2[i]) c=c*a%F;
a=a*a%F;
}
return c;
}
map<ll,ll> d;
int main()
{
// freopen("c.in","r",stdin);
// freopen(".out","w",stdout);

int T;cin>>T;

while(T--) {
d.clear();
cin>>n;
For(i,n) scanf("%I64d",&a[i]);

ll ans=0;
ll now = 1;

For(i,n) {
if (d.find(a[i])==d.end()) d[a[i]]=0;

ans+=a[i]*pow2(2,n-i)%F*((now-d[a[i]]+F ) %F )%F;
ans%=F;

ll p=pow2(2,i-1);
d[a[i]]=(d[a[i]] + p )%F;
now=(now + p)%F;
}
printf("%I64d\n",ans%F);
}

return 0;
}```