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
1 #include<cstdio> 2 #include<algorithm> 3 #include<cstring> 4 #include<vector> 5 using namespace std; 6 #define fi first 7 #define se second 8 #define mp make_pair 9 #define pb push_back 10 typedef long long ll; 11 typedef unsigned long long ull; 12 typedef pair<int,int> pii; 13 const ll md=19940417; 14 ll n,m,ans,a1,a2; 15 ll Mod(ll x,ll md=md) 16 { 17 if(x>=0) return x%md; 18 else if(x%md==0) return 0; 19 else return md+x%md; 20 } 21 ll calc(ll x) 22 { 23 return (x)*(x+1)%md*(2*x+1)%md*3323403%md; 24 } 25 int main() 26 { 27 ll i,j; 28 scanf("%lld%lld",&n,&m); 29 if(n>m) swap(n,m); 30 31 32 // { 33 // ll ams=0; 34 // for(ll i=1;i<=n;i++) 35 // for(ll j=1;j<=m;j++) 36 // if(i!=j) 37 // ams=Mod(ams+(n-n/i*i)*(m-m/j*j)); 38 // printf("%lld",ams); 39 // return 0; 40 // } 41 42 43 for(i=1;i<=n;i=j+1) 44 { 45 j=n/(n/i); 46 a1=Mod(a1+Mod((i+j)*(j-i+1)/2)*(n/i)); 47 } 48 for(i=1;i<=m;i=j+1) 49 { 50 j=m/(m/i); 51 a2=Mod(a2+Mod((i+j)*(j-i+1)/2)*(m/i)); 52 } 53 //printf("a%lld %lld\n",a1,a2); 54 55 ans=Mod(ans+n*n%md*m%md*m%md); 56 ans=Mod(ans-n*n%md*a2%md); 57 ans=Mod(ans-m*m%md*a1%md); 58 ans=Mod(ans+a1*a2%md); 59 60 ans=Mod(ans-n*n%md*m%md); 61 { 62 ll t=0; 63 for(i=1;i<=n;i=j+1) 64 { 65 j=min(n,m/(m/i)); 66 t=Mod(t+Mod((i+j)*(j-i+1)/2)*(m/i)); 67 } 68 ans=Mod(ans+n*t%md); 69 } 70 ans=Mod(ans+m*a1%md); 71 { 72 ll t=0; 73 for(i=1;i<=n;i=j+1) 74 { 75 j=min(n/(n/i),m/(m/i)); 76 t=Mod(t+Mod(calc(j)-calc(i-1))*(n/i)%md*(m/i)); 77 } 78 //printf("t%lld\n",t); 79 ans=Mod(ans-t); 80 } 81 82 printf("%lld",ans); 83 return 0; 84 }
