63 lines
1.6 KiB
Factor
63 lines
1.6 KiB
Factor
! Copyright (c) 2007 Samuel Tardieu, Aaron Schaefer.
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! See http://factorcode.org/license.txt for BSD license.
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USING: io.files math.parser namespaces project-euler.common
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io.encodings.ascii sequences splitting ;
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IN: project-euler.067
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! http://projecteuler.net/index.php?section=problems&id=67
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! DESCRIPTION
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! -----------
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! By starting at the top of the triangle below and moving to adjacent numbers
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! on the row below, the maximum total from top to bottom is 23.
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! 3
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! 7 5
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! 2 4 6
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! 8 5 9 3
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! That is, 3 + 7 + 4 + 9 = 23.
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! Find the maximum total from top to bottom in triangle.txt (right click and
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! 'Save Link/Target As...'), a 15K text file containing a triangle with
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! one-hundred rows.
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! NOTE: This is a much more difficult version of Problem 18. It is not possible
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! to try every route to solve this problem, as there are 2^99 altogether! If you
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! could check one trillion (10^12) routes every second it would take over twenty
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! billion years to check them all. There is an efficient algorithm to solve it. ;o)
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! SOLUTION
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! --------
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! Propagate from bottom to top the longest cumulative path as is done in
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! problem 18.
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<PRIVATE
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: source-067 ( -- seq )
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"resource:extra/project-euler/067/triangle.txt"
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ascii file-lines [ " " split [ string>number ] map ] map ;
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PRIVATE>
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: euler067 ( -- answer )
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source-067 propagate-all first first ;
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! [ euler067 ] 100 ave-time
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! 20 ms ave run time - 2.12 SD (100 trials)
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! ALTERNATE SOLUTIONS
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! -------------------
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: euler067a ( -- answer )
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source-067 max-path ;
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! [ euler067a ] 100 ave-time
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! 21 ms ave run time - 2.65 SD (100 trials)
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SOLUTION: euler067a
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