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;
}