期望 40

code1:

#include<bits/stdc++.h>
using namespace std;
long long a[]={3,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997};
int b[1008];
bool ok(int x,int y)
{
	int gcd=__gcd(x,y);
	y/=gcd;
	if(b[y]!=-1) return b[y];
	for(int i=0;a[i]<=y;i++)
	{
		if(y%a[i]==0) 
		{
			b[y]=0;
			return 0;
		}
	}
	b[y]=1;
	return 1;
}
long long n,ans;
int main()
{
	memset(b,-1,sizeof(b));
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=n;j++)
		{
			if(ok(i,j))
			{
				//cout<<i<<' '<<j<<endl; 
				ans++;
			}
		}	
	}
	cout<<ans;
	return 0;
} 

code2:

#include<bits/stdc++.h>
using namespace std;
long long n,ans;
map<pair<long long,long long>,bool> mp;
int main() 
{
	cin>>n;
	for(long long i=1;i<=n;i*=2)
	{
		for(long long j=1;j<=n;j*=5)
		{
			if(i*j>n) break;
			for(long long k=1;k<=n;k++)
			{
				if(i*j*k>n) break;
				for(long long l=1;l<=n;l++)
				{
					if(k*l>n) break;
					if(mp[make_pair(k*l,i*j*k)]) continue;
					mp[make_pair(k*l,i*j*k)]=1;
					ans++;
				}
			}
		}
	}
	cout<<ans;
	return 0;
}

code1并不能保证每次循环都是答案，但2可以，为啥2比1慢好多啊？