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annotate day11b.rb @ 27:6b58ddfaed38

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Add Day 18 part 1 solution using line crossing
author IBBoard <dev@ibboard.co.uk>
date Tue, 02 Jan 2024 16:04:33 +0000
parents ddb69833346c
children
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18
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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 EXPANSION_FACTOR = 1000000
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14
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15 input_space = File.open(file, "r").each_line(chomp: true).map(&:each_char).map(&:to_a)
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16
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17 first, *rest = input_space
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18 open_columns = first.zip(*rest).each_with_index.map {|col, idx| col.all? {|cell| cell == OPEN_SPACE} ? idx : nil}.compact
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19 open_rows = input_space.each_with_index.map {|row, idx| row.all? {|cell| cell == OPEN_SPACE} ? idx : nil}.compact
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20
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21
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22 galaxies = input_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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23 galactic_distances = galaxies.combination(2).map do |a, b|
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24 x_1, x_2 = [a[0], b[0]].minmax
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25 y_1, y_2 = [a[1], b[1]].minmax
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26 expanded_cols = ((x_1..x_2).to_a & open_columns).length
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27 expanded_rows = ((y_1..y_2).to_a & open_rows).length
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28
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29 # Avoid double-counting the expanded cell by subtracting the number of columns first rather any complex logic
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30 x_2 - x_1 + - expanded_cols + (expanded_cols * EXPANSION_FACTOR) + y_2 - y_1 + - expanded_rows + (expanded_rows * EXPANSION_FACTOR)
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31 end
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32 puts galactic_distances.sum