bzoj1257

数学分块

按照k/i分成sqrt(n)块，块与块之间用等差数列算一算

/**************************************************************     Problem: 1257     User: syh0313     Language: C++     Result: Accepted     Time:20 ms     Memory:1288 kb ****************************************************************/   #include <iostream> #include <cstdio> #include <cstdlib> using namespace std; long long n,k,ans,now; int main() {     scanf("%lld%lld",&n,&k);     if (n>=k) {ans=(n-k)*k; n=k;}     ans+=n*k;     //printf("%lld\n",ans);     for (long long i=1;i<=n;)     {         long long l=i,r=k/(k/i);         //printf("%lld %lld %lld\n",l,r,(k/i)*(l+r)*(r-l+1)/2);         r=min(r,n);         ans-=(k/i)*(l+r)*(r-l+1)/2;         i=r+1;     }     printf("%lld\n",ans); return 0; }