全排列算法(Using c++ template):

全排列算法(Using c++ template):

这是一个全排列算法的C++模板, 与STL中泛型算法next_permutation的功能是一样的。

template < typename T >
bool _next_permutation( T *first, T *last );
#define N 8
int main(int argc, char* argv[])
{
        int i;
        int y = 1;//序号
        char a[N];
        for ( i=0; i<N; i++ )
        {
                a[i] = i + 1 + 64 + 32;
        }

        long t0 = time( NULL );
        do
        {
                cout << y << "　--->　";
                for ( i = 0; i<N; i++ ) cout << a[i];
                cout << endl;

                y++;
        }while( _next_permutation( &a[0], &a[N] ) );
        long t1 = time( NULL ) - t0;
        cout << t1 << endl;//当N为8时耗时130秒，与泛型算法next_permutation用时一样

        return 0;
}

template < typename T >
bool _next_permutation( T *first, T *last )
{
        int i;
        int j;
        int x = -1;
        int rang = last - first;
       
        for ( i=0; i<rang-1; i++ )
        {
                if ( *( first+i ) <= *( first+i+1 ) )
                {
                        x = i;
                }
        }

        if ( x != -1 )
        {
                for ( i=x; i<rang; i++ )
                {
                        if ( *( first+x ) <= *( first+i ) )
                        {
                                j = i;
                        }
                }

                _swap( *( first+x ), *( first+j ) );

                for ( i=x+1; i<rang; i++ )
                {
                        if ( i != rang + x - i )
                        {
                                int nSwap = rang + x - i;
                                _swap( *( first+i ), *( first+ ( rang+x-i ) ) );
                        }
                        if ( ( i + 1 ) * 2 > rang + x )
                        {
                                break;
                        }
                }
        }

        if ( -1 == x ) return false;
        else return true;
}

template < typename T >
void _swap( T &a, T &b )
{
        a = a + b;
        b = a - b;
        a = a - b;
}