Number With The Given Amount Of Divisors CodeForces - 27E【反素数+dfs】

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思路：反素数及其在OI中的应用 里面第一种类型

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
#define LL unsigned long long
#define INF 0x3f3f3f3f3f3f3f3f
#define MAXN 1005
int p[]={2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53};
int n;
LL ans=INF;
void dfs(int i/*第几个质数*/,LL tmp/*答案*/,int num/*因子个数*/)
{
	if(num>n||i>=16) return ;
	if(num==n&&tmp<ans) ans=tmp;
	for(int j=1;j<=64;j++)//2^64>10^18
	{
		if(ans<tmp) break;
		tmp*=p[i];
		dfs(i+1,tmp,num*(j+1));
	}
}
int main()
{
	scanf("%d",&n);
	dfs(0,1,1);
	printf("%I64d\n",ans);
	return 0;
}