198. 反素数数论

Posted 2021-11-04 幽殇默

https://www.acwing.com/problem/content/description/200/
2*3*5*7*11*13*17*19*23*>2*10⁹
且质数的次数是依次递减的

#include<bits/stdc++.h>
using namespace std;
typedef long long int LL;
LL p[10]={2,3,5,7,11,13,17,19,23};
LL maxv,ans,n;
void dfs(LL index,LL last,LL sum,LL cnt)
{
    if(cnt>ans||sum<maxv&&cnt==ans) maxv=sum,ans=cnt;
    if(index==9) return;
    for(LL i=1;i<=last;i++)
    {
        if(sum*p[index]>n) break;
        sum*=p[index];
        dfs(index+1,i,sum,cnt*(i+1));
    }
}
int main(void)
{
    cin>>n;
    dfs(0,30,1,1);
    cout<<maxv<<endl;
    return 0;
}