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annotate day11.rb @ 18:ddb69833346c

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Implement day 11 distance finding in space "shortest distance" is simplified by it being cardinal directions, so it's the same as taking the right-angle between them. The Part 1 space expansion was quite clean, but the Part 2 approach generalises it to something even nicer.
author IBBoard <dev@ibboard.co.uk>
date Mon, 11 Dec 2023 20:08:47 +0000
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18
ddb69833346c Implement day 11 distance finding in space
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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")
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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 OPEN_SPACE = "."
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12 GALAXY = "#"
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13
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14 input_space = File.open(file, "r").each_line(chomp: true).map(&:each_char).map(&:to_a)
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15
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16 first, *rest = input_space
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17 open_columns = first.zip(*rest).map {|col| col.all? {|cell| cell == OPEN_SPACE}}
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18
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19 expanded_space = input_space.flat_map do |row|
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20 new_row = row.zip(open_columns).flat_map {|cell, is_open| is_open ? [cell, cell] : [cell]}
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21 if row.all? {|cell| cell == OPEN_SPACE} then [new_row, new_row] else [new_row] end
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22 end
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23
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24 galaxies = expanded_space.each_with_index.flat_map {|row, y| row.each_with_index.map {|cell, x| [x, y] if cell == GALAXY}}.compact
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25 galactic_distances = galaxies.combination(2).map {|a, b| (a[0] - b[0]).abs + (a[1] - b[1]).abs}
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26 puts galactic_distances.sum