BZOJ 1257[CQOI2007]余数之和sum | 数论

题目:

http://www.lydsy.com/JudgeOnline/problem.php?id=1257

题解:

不知道咋做的

#include<cstdio>
#include<algorithm>
typedef long long ll;
ll ans,n,k;
int main()
{
scanf("%lld%lld",&n,&k);
if (n>k)
{
ans=(n-k)*k,n=k;
}
ll r;
for (ll i=1;i<=n;i=r+1)
{
ll t=k/i;r=k/t;
if (r>=n) r=n;
ans+=(r-i+1ll)*k-(r-i+1ll)*(i+r)/2*t;
}
printf("%lld\n",ans);
return 0;
}