If b = " " i . e . , an empty string . There is only one way to transform ( remove all characters )
if ( m == 0 ) return 1 ; int [ , ] dp = new int [ m , n ] ; for ( int i = 0 ; i < m ; i ++ ) for ( int j = 0 ; j < n ; j ++ ) dp [ i , j ] = 0 ;