34 lines
668 B
Factor
34 lines
668 B
Factor
! Copyright (c) 2007 Aaron Schaefer.
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! See http://factorcode.org/license.txt for BSD license.
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USING: kernel math math.combinatorics project-euler.common ;
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IN: project-euler.015
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! http://projecteuler.net/index.php?section=problems&id=15
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! DESCRIPTION
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! -----------
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! Starting in the top left corner of a 2x2 grid, there are 6 routes (without
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! backtracking) to the bottom right corner.
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! How many routes are there through a 20x20 grid?
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! SOLUTION
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! --------
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<PRIVATE
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: grid-paths ( n -- n )
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dup 2 * swap nCk ;
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PRIVATE>
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: euler015 ( -- answer )
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20 grid-paths ;
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! [ euler015 ] 100 ave-time
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! 0 ms ave run time - 0.2 SD (100 trials)
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SOLUTION: euler015
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