CF 576A 猜数

A给出一个数x，B每次猜一个y，A回答B，x是否可以被y整除，求出要猜的最小次数和需要猜的数。

枚举每个素数p，可以知道如果p^k<=n，则p^k一定需要选

Sample test(s)
input
4
output
3
2 4 3
input
6
output
4
2 4 3 5

 # include <iostream>
 # include <cstdio>
 # include <cstring>
 # include <algorithm>
 # include <string>
 # include <cmath>
 # include <queue>
 # include <list>
 # define LL long long
 using namespace std ;

 int ans[] ;

 bool isp (int val )
 {
      int i ;
      if (val == )
        return  ;
      for (i =  ; i*i <= val ; i++)
      {
          if (val % i == )
              return  ;
      }
      return  ;

 }

 int main()
 {
     //freopen("in.txt","r",stdin) ;
     int n ;
     while(scanf("%d",&n ) != EOF)
     {
         int i ;
         int l =  ;
         if (n == )
         {
             printf("0\n") ;
             continue ;
         }

         for (i =  ; i <= n ; i++)
         {
             if (isp(i) == )
                 continue ;
             int p = i ;
             while(p <= n)
             {
                 ans[l] = p ;
                 l++ ;
                 p *= i ;
             }
         }
         printf("%d\n" , l) ;
         for (i =  ; i < l- ; i++)
             printf("%d " , ans[i]) ;
         printf("%d\n" , ans[i]) ;
     }

     return ;
 }