Alphabet Bit Mask - String Compares - String Hash

[kevin]

This block of code generates a mask of used characters (restricted to the alphabet) based on a given input string. The technique employed involves using bits 0 to 25 of a 32-bit integer to represent a flag for the presence of each character in the alphabet.

If you have a requirement to compare user input with a dictionary of words, you could store the bitmasks of the words as a hash. If two words share the same mask, they at least contain the same set of letters. Then, you can compare the actual strings to determine if they are an exact match.

PlayBASIC Code: [Select]

   /*

     This block of code generates a mask of used characters
    (restricted to the alphabet) based on a given input string.
    The technique employed involves using bits 0 to 25 of a
    32-bit integer to represent a flag for the presence of
    each character in the alphabet.

      If you have a requirement to compare user input with a
    dictionary of words, you could store the bitmasks of the
    words as a hash. If two words share the same mask, they at
    least contain the same set of letters. Then, you can compare
    the actual strings to determine if they are an exact match.

   */


   for lp=asc("A") to asc("Z")
      print bin$(Alphabet_BitMASK(Chr$(lp)))
      s$+=chr$(lp)
   next

   print bin$(AlphaBet_BitMASK(s$))

   Sync
   waitkey
   
   


Function Alphabet_BitMASK(ThisString$)
         
         ThisString$=upper$(ThisString$)
         
         For lp=1 to Len(ThisString$)
               ThisCHR = mid(ThisString$,lp)-asc("A")
               BitMASK |= 1 << ThisCHR
         next
   
EndFunction BitMASK