@[qinxili](/user/663740) 数组开小了
by sybnb @ 2024-02-08 21:50:55
aa也开错了
by sybnb @ 2024-02-08 21:53:50
# AC Code
```cpp
#include <bits/stdc++.h>
using namespace std;
const long long N=150000,aa=1e9+7;
long long a[N],mx=0,ms=99999999999,as=0;
int main()
{
int n;
cin>>n;
for(long long i=1; i<=n; i++)
{
long long x;
cin>>x;
a[x]++;
if(mx<x)
{
mx=x;
}
if(ms>x)
{
ms=x;
}
}
for(long long i=ms+1; i<=mx; i++)
{
if(a[i]>=2)
{
for(long long j=ms; j<=i/2; j++)
{
if(j!=i-j)
{
as+=a[i]*(a[i]-1)*a[j]*a[i-j]/2%aa;
}
else if(a[j]>=2 && j*2==i)
{
as+=a[i]*(a[i]-1)*a[i/2]*(a[i/2]-1)/4%aa;
}
}
as%=aa;
}
}
cout<<as;
return 0;
}
```
by sybnb @ 2024-02-08 21:54:20