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towers of hanoi

Source : Free On-Line Dictionary of Computing

Towers of Hanoi
     
         A classic computer science problem, invented by
        Edouard Lucas in 1883, often used as an example of
        {recursion}.
     
        "In the great temple at Benares, says he, beneath the dome
        which marks the centre of the world, rests a brass plate in
        which are fixed three diamond needles, each a cubit high and
        as thick as the body of a bee.  On one of these needles, at
        the creation, God placed sixty-four discs of pure gold, the
        largest disc resting on the brass plate, and the others
        getting smaller and smaller up to the top one.  This is the
        Tower of Bramah.  Day and night unceasingly the priests
        transfer the discs from one diamond needle to another
        according to the fixed and immutable laws of Bramah, which
        require that the priest on duty must not move more than one
        disc at a time and that he must place this disc on a needle so
        that there is no smaller disc below it.  When the sixty-four
        discs shall have been thus transferred from the needle on
        which at the creation God placed them to one of the other
        needles, tower, temple, and Brahmins alike will crumble into
        dust, and with a thunderclap the world will vanish."
     
        The recursive solution is: Solve for n-1 discs recursively,
        then move the remaining largest disc to the free needle.
     
        Note that there is also a non-recursive solution: On
        odd-numbered moves, move the smallest sized disk clockwise.
        On even-numbered moves, make the single other move which is
        possible.
     
        ["Mathematical Recreations and Essays", W W R Ball, p. 304]
     
        {The rec.puzzles Archive
        (http://rec-puzzles.org/sol.pl/induction/hanoi)}.
     
        (2003-07-13)
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