MagicWords (SRM433 Div2 500)

MagicWords (SRM433 Div2 500)

题目链接：http://www.topcoder.com/stat?c=problem_statement&pm=10195

直接按描述生成S的所有排列，并计数就可以了。用map缓存一下计算结果，不然会超时
在一个整数vector上用next_permutation算法来生成所有排列的索引。

#include  < vector >
#include  < algorithm >
#include  < sstream >
#include  < string >
#include  < iostream >
#include  < map >

using   namespace  std;

          class  MagicWords
              { 
               public :

               map < string , bool >  m;

               int  count(vector  < string >  s,  int  k) 
                  {
                       int  ret  =   0 ;

                      vector < int >  v(s.size());
                      
                       for ( int  i = 0 ;i < v.size(); ++ i)
                          v[i]  =  i;

                      m.clear();
                   
                       do {

                           string  str;
                           for ( int  i = 0 ;i < v.size(); ++ i){
                              str += s[v[i]]; 
                          }                        
                           if ( isMagic(str,k) )
                              ret ++ ;

                      } while ( next_permutation(v.begin(),v.end()) );


                       return  ret;
                  } 

               bool  isMagic( string   & str, int  k){

                   if (m.find(str) != m.end())
                       return  m[str];

                   int  cnt  =   1 ;
                   int  len  =  str.size();
                   for ( int  i = 1 ;i < len; ++ i){
                       bool  ok  =   true ;
                       for ( int  j = 0 ;j < len; ++ j){
                           if ( str[j]  !=  str[(j + i) % len]){
                              ok  =   false ;
                               break ;
                          }
                      }

                       if (ok)
                       cnt ++ ;
                  }

                  m[str]  =   (cnt == k);

                   return  cnt == k;
              }
 }