UVa 1326 - Jurassic Remains(枚举子集+中途相遇法)

训练指南p.59

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <map>

using namespace std;

const int MAXN = ;

int N;
int A[MAXN];
char str[];
map<int , int> table;

int bitcount( int x )
{
    int res = ;
    while ( x )
    {
        if ( x &  ) ++res;
        x >>= ;
    }
    return res;
}

int main()
{
    while ( scanf( "%d", &N ) ==  )
    {
        for ( int i = ; i < N; ++i )
        {
            scanf( "%s", str );
            A[i] = ;
            for ( int j = ; str[j]; ++j )
                A[i] |= (  << ( str[j] - 'A' ) );
        }

        table.clear();

        int n1 = N / , n2 = N - n1;
        for ( int i = ; i < (  << n1 ); ++i )
        {
            int tmp = ;
            for ( int j = ; j < n1; ++j )
            if ( i & (  << j ) )
                tmp ^= A[j];
            if ( !table.count(tmp) || bitcount(i) > bitcount( table[tmp] ) ) table[tmp] = i;
        }

        int ans = ;
        for ( int i = ; i < (  << n2 ); ++i )
        {
            int tmp = ;
            for ( int j = ; j < n2; ++j )
            if ( i & (  << j ) ) tmp ^= A[ n1 + j ];
            if ( table.count(tmp) && bitcount(ans) < bitcount(i) + bitcount(table[tmp]) )
                ans = ( i << n1 ) | table[tmp];
        }

        printf("%d\n", bitcount(ans) );
        bool first = false;
        for ( int i = ; i < N; ++i )
        if ( ans & (  << i ) )
        {
            if ( first ) putchar(' ');
            printf("%d", i + );
            first = true;
        }
        puts("");
    }
    return ;
}