尝试使用递归函数解决问题+set容器

解题思路:

注意事项:

参考代码:

#include<iostream>

#include<set>

using namespace std ;

int ko ( int n , set<int>&x )

{

         if ( n == 2 )

         {

                 x.insert(2) ;

                 return 0 ;

         }

         else if ( n < 2 ) return 1 ;

         else

         {

                 if ( n%2 == 0 ) x.insert(n) ;

                 return ko( n-1, x ) ;

         }

}

int main ( )

{

         int n = 0 ;

         cin >> n ;

         set<int>x ;

        if (!ko ( n-1 , x ) )

             for ( auto it : x )

             {

                      cout << it << endl ;

             }

         return 0 ;

}