【SPJ6285 NGM2 - Another Game With Numbers】 题解

题目链接：https://www.luogu.org/problemnew/show/SP6285

唉好久之前校内模拟赛的题目

嘴上说着明白但是实现起来我的位运算太丑陋了啊！

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define ll long long
using namespace std;
const int maxn = 300;
ll n, k, a[maxn], ans;
ll gcd(ll x, ll y)
{
	if(x % y == 0) return y;
	else return gcd(y, x%y);
}
ll lcm(ll x, ll y)
{
	return x / gcd(x,y) * y;
}
int main()
{
	ios::sync_with_stdio(false);
	cin>>n>>k;
	for(ll i = 0; i < k; i++) cin>>a[i];
	for(ll i = 1; i < (1 << k); i++)
	{
		ll res = 1, flag = 0;
		for(ll j = 0; j < k; j++)
		{
			if(i & (1 << j)) 
			{ 
				res = lcm(res, a[j]);
				flag++;
			}
		}
		if(flag & 1) ans += (n/res);
		else ans -= (n/res);
	}
	cout<<n-ans;
	return 0;
}