洛谷 P2260 [清华集训2012]模积和 || bzoj2956

https://www.lydsy.com/JudgeOnline/problem.php?id=2956

https://www.luogu.org/problemnew/show/P2260

暴力推式子即可

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<vector>
 using namespace std;
 #define fi first
 #define se second
 #define mp make_pair
 #define pb push_back
 typedef long long ll;
 typedef unsigned long long ull;
 typedef pair<int,int> pii;
 const ll md=;
 ll n,m,ans,a1,a2;
 ll Mod(ll x,ll md=md)
 {
     if(x>=)    return x%md;
     else if(x%md==)    return ;
     else    return md+x%md;
 }
 ll calc(ll x)
 {
     return (x)*(x+)%md*(*x+)%md*%md;
 }
 int main()
 {
     ll i,j;
     scanf("%lld%lld",&n,&m);
     if(n>m)    swap(n,m);

 //    {
 //        ll ams=0;
 //        for(ll i=1;i<=n;i++)
 //            for(ll j=1;j<=m;j++)
 //                if(i!=j)
 //                ams=Mod(ams+(n-n/i*i)*(m-m/j*j));
 //        printf("%lld",ams);
 //        return 0;
 //    }

     for(i=;i<=n;i=j+)
     {
         j=n/(n/i);
         a1=Mod(a1+Mod((i+j)*(j-i+)/)*(n/i));
     }
     for(i=;i<=m;i=j+)
     {
         j=m/(m/i);
         a2=Mod(a2+Mod((i+j)*(j-i+)/)*(m/i));
     }
     //printf("a%lld %lld\n",a1,a2);

     ans=Mod(ans+n*n%md*m%md*m%md);
     ans=Mod(ans-n*n%md*a2%md);
     ans=Mod(ans-m*m%md*a1%md);
     ans=Mod(ans+a1*a2%md);

     ans=Mod(ans-n*n%md*m%md);
     {
         ll t=;
         for(i=;i<=n;i=j+)
         {
             j=min(n,m/(m/i));
             t=Mod(t+Mod((i+j)*(j-i+)/)*(m/i));
         }
         ans=Mod(ans+n*t%md);
     }
     ans=Mod(ans+m*a1%md);
     {
         ll t=;
         for(i=;i<=n;i=j+)
         {
             j=min(n/(n/i),m/(m/i));
             t=Mod(t+Mod(calc(j)-calc(i-))*(n/i)%md*(m/i));
         }
         //printf("t%lld\n",t);
         ans=Mod(ans-t);
     }

     printf("%lld",ans);
     return ;
 }