HDU 2920 分块底数优化 暴力

其实和昨天写的那道水题是一样的，注意爆LL

$1<=n,k<=1e9$，$\sum\limits_{i=1}^{n}(k \mod i) = nk - \sum\limits_{i=1}^{min(n,k)}\lfloor\frac{k}{i}\rfloor i$

/** @Date    : 2017-09-21 19:55:31
  * @FileName: HDU 2620 分块底数优化 暴力.cpp
  * @Platform: Windows
  * @Author  : Lweleth (SoungEarlf@gmail.com)
  * @Link    : https://github.com/
  * @Version : $Id$
  */
#include <bits/stdc++.h>
#define LL long long
#define PII pair
#define MP(x, y) make_pair((x),(y))
#define fi first
#define se second
#define PB(x) push_back((x))
#define MMG(x) memset((x), -1,sizeof(x))
#define MMF(x) memset((x),0,sizeof(x))
#define MMI(x) memset((x), INF, sizeof(x))
using namespace std;

const int INF = 0x3f3f3f3f;
const int N = 1e5+20;
const double eps = 1e-8;

int main()
{
	LL n, k;
	while(cin >> n >> k)
	{
		LL ans = n * k;
		int ma = min(n, k);
		for(LL i = 1, j; i <= ma; i = j + 1)
		{
			j = (k / (k / i));
			if(j > ma)
				j = ma;
			LL t = 0;
			if((i + j) % 2)//注意溢出的问题
				t = (j - i + 1) / 2LL * (i + j);
			else
				t = (i + j) / 2LL * (j - i + 1);
			ans -= t * (k / i);
		}
		printf("%lld\n", ans);
	}
    return 0;
}