30 lines
769 B
Factor
30 lines
769 B
Factor
! Copyright (c) 2012 Anonymous
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! See http://factorcode.org/license.txt for BSD license.
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USING: kernel sequences math math.combinatorics formatting io locals ;
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IN: rosetta-code.n-queens
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! http://rosettacode.org/wiki/N-queens_problem
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! Solve the eight queens puzzle. You can extend the problem to
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! solve the puzzle with a board of side NxN.
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:: safe? ( board q -- ? )
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[let q board nth :> x
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q <iota> [
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x swap
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[ board nth ] keep
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q swap -
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[ + = not ]
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[ - = not ] 3bi and
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] all?
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] ;
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: solution? ( board -- ? )
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dup length <iota> [ dupd safe? ] all? nip ;
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: queens ( n -- l )
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<iota> all-permutations [ solution? ] filter ;
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: queens. ( n -- )
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queens [ [ 1 + "%d " printf ] each nl ] each ;
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