38 lines
932 B
Factor
38 lines
932 B
Factor
! Copyright (c) 2007 Aaron Schaefer, Daniel Ehrenberg.
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! See http://factorcode.org/license.txt for BSD license.
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USING: hashtables kernel math math.functions math.ranges project-euler.common
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sequences sorting sets ;
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IN: project-euler.004
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! http://projecteuler.net/index.php?section=problems&id=4
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! DESCRIPTION
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! -----------
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! A palindromic number reads the same both ways. The largest palindrome made
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! from the product of two 2-digit numbers is 9009 = 91 * 99.
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! Find the largest palindrome made from the product of two 3-digit numbers.
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! SOLUTION
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! --------
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<PRIVATE
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: source-004 ( -- seq )
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100 999 [a,b] [ 10 divisor? ] reject ;
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: max-palindrome ( seq -- palindrome )
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natural-sort [ palindrome? ] find-last nip ;
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PRIVATE>
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: euler004 ( -- answer )
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source-004 dup [ * ] cartesian-map combine max-palindrome ;
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! [ euler004 ] 100 ave-time
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! 1164 ms ave run time - 39.35 SD (100 trials)
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SOLUTION: euler004
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