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annotate day2b.rb @ 39:0e17e4bd97a9 default tip

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Rewrite as four-dimensional route finding The grid isn't just a 2D grid. The constraints make it 4D: * X * Y * Last direction * Number of steps in that direction By tracking all four dimensions, we can find the shortest route for _all_ combinations of the constraint. Previously, we were dropping routes that were currently longer but ended up shorter because they could take subsequent steps that other routes couldn't.
author IBBoard <dev@ibboard.co.uk>
date Sun, 22 Sep 2024 11:30:53 +0100
parents 49dd1ae93696
children
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49dd1ae93696 Implement day 2 with map and reduce
IBBoard <dev@ibboard.co.uk>
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1 #! /usr/bin/env ruby
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2
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3 if ARGV.length != 1
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4 abort("Incorrect arguments - needs input file")
49dd1ae93696 Implement day 2 with map and reduce
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5 elsif not File.exist? (ARGV[0])
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6 abort("File #{ARGV[0]} did not exist")
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7 end
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8
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9 file = ARGV[0]
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10
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11 sum = 0
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12 File.open(file, "r").each_line do |line|
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13 _, all_picks = line.split(":")
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14 sum += all_picks.split(";").map do |pick|
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15 pick.split(",").to_h { |colour_pick| colour_pick.strip.split(" ").reverse }.transform_values(&:to_i)
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16 end.reduce(Hash.new) {|reduced,obj| reduced.merge(obj) { |key,val1,val2| val1 > val2 ? val1 : val2 }}.values.reduce(1, :*)
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17 end
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18
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19 puts sum