[除法分块] BZOJ1257: [CQOI2007]余数之和sum

题意

题解

#include<cstdio>
#include<algorithm>
using namespace std;
typedef long long LL;
LL n,m,ans;
int main(){
scanf("%lld%lld",&m,&n);
for(LL i=1,nxt;i<=min(m,n);i=nxt+1){
nxt=n/(n/i); nxt=min(nxt,min(n,m));
ans+=(i+nxt)*(nxt-i+1)/2*(n/i);
}
ans=n*m-ans;
printf("%lld\n",ans);
return 0;
}