kkck: A solver for Kriss Kross puzzles

# - - -   P u z z l e . _ _ r e d u c e S l o t

    def __reduceSlot ( self, cell, slot, letterSet ):
        '''Remove choices for a slot that don't have given letters.

          [ (cell is a Cell in self) and
            (slot is a Slot in self that contains cell) and
            (letterSet is a set of one-character strings) ->
              self.__wordBank  :=  self.__wordBank - (choices for
                  slots whose characters at cell's position
                  are not in letterSet ]
        '''

We first materialize the set of choices into a separate list, wordList. We'll also need to know the position (k) of the letter relative to the start of the slot; that is computed by Section 59, “Slot.findCoord(): Puzzle position to slot position”.

        #-- 1 --
        # [ wordList  :=  list of word choices in self.__wordBank
        #       for slot, as a list of Word instances
        #   cellx  :=  position of cell relative to slot ]
        wordList = [ word
                     for word in
                     self.__wordBank.genSlotChoices ( slot ) ]
        cellx = slot.findCoord ( cell.coord )

Next, work through wordList and, for each choice that has a letter at the position cellx that is not in letterSet, we remove it from the slot choices by calling Section 68, “WordBank.isNot(): Remove one word from a slot's list of choices”.

        #-- 2 --
        # [ self.__wordBank  :=  self.__wordBank - (choices for slot
        #       that have letters in position cellx that are not in
        #       letterSet ]
        for word in wordList:
            #-- 2 body --
            # [ if word[cellx] is not in letterSet ->
            #     self.__wordBank  :=  self.__wordBank - (choice
            #         of word for slot)
            if word[cellx] not in letterSet:
                if VERBOSE:
                    print ( "*** Removing %s from %s because "
                        "word [%d] is not in %r." %
                        (word, slot, cellx, ''.join(list(letterSet))) )
                self.__wordBank.isNot ( slot, word )