64 lines
1.4 KiB
Factor
64 lines
1.4 KiB
Factor
! Copyright (c) 2008 Aaron Schaefer.
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! See http://factorcode.org/license.txt for BSD license.
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USING: kernel math project-euler.common ;
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IN: project-euler.031
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! http://projecteuler.net/index.php?section=problems&id=31
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! DESCRIPTION
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! -----------
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! In England the currency is made up of pound, £, and pence, p, and there are
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! eight coins in general circulation:
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! 1p, 2p, 5p, 10p, 20p, 50p, £1 (100p) and £2 (200p).
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! It is possible to make £2 in the following way:
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! 1×£1 + 1×50p + 2×20p + 1×5p + 1×2p + 3×1p
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! How many different ways can £2 be made using any number of coins?
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! SOLUTION
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! --------
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<PRIVATE
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: 1p ( m -- n )
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drop 1 ;
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: 2p ( m -- n )
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dup 0 >= [ [ 2 - 2p ] [ 1p ] bi + ] [ drop 0 ] if ;
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: 5p ( m -- n )
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dup 0 >= [ [ 5 - 5p ] [ 2p ] bi + ] [ drop 0 ] if ;
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: 10p ( m -- n )
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dup 0 >= [ [ 10 - 10p ] [ 5p ] bi + ] [ drop 0 ] if ;
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: 20p ( m -- n )
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dup 0 >= [ [ 20 - 20p ] [ 10p ] bi + ] [ drop 0 ] if ;
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: 50p ( m -- n )
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dup 0 >= [ [ 50 - 50p ] [ 20p ] bi + ] [ drop 0 ] if ;
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: 100p ( m -- n )
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dup 0 >= [ [ 100 - 100p ] [ 50p ] bi + ] [ drop 0 ] if ;
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: 200p ( m -- n )
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dup 0 >= [ [ 200 - 200p ] [ 100p ] bi + ] [ drop 0 ] if ;
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PRIVATE>
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: euler031 ( -- answer )
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200 200p ;
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! [ euler031 ] 100 ave-time
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! 3 ms ave run time - 0.91 SD (100 trials)
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! TODO: generalize to eliminate duplication; use a sequence to specify denominations?
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SOLUTION: euler031
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