Mercurial > repos > other > adventofcode2023
comparison day11b.rb @ 18:ddb69833346c
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> |
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date | Mon, 11 Dec 2023 20:08:47 +0000 |
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17:92144824cbb7 | 18:ddb69833346c |
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1 #! /usr/bin/env ruby | |
2 | |
3 if ARGV.length != 1 | |
4 abort("Incorrect arguments - needs input file") | |
5 elsif not File.exist? (ARGV[0]) | |
6 abort("File #{ARGV[0]} did not exist") | |
7 end | |
8 | |
9 file = ARGV[0] | |
10 | |
11 OPEN_SPACE = "." | |
12 GALAXY = "#" | |
13 EXPANSION_FACTOR = 1000000 | |
14 | |
15 input_space = File.open(file, "r").each_line(chomp: true).map(&:each_char).map(&:to_a) | |
16 | |
17 first, *rest = input_space | |
18 open_columns = first.zip(*rest).each_with_index.map {|col, idx| col.all? {|cell| cell == OPEN_SPACE} ? idx : nil}.compact | |
19 open_rows = input_space.each_with_index.map {|row, idx| row.all? {|cell| cell == OPEN_SPACE} ? idx : nil}.compact | |
20 | |
21 | |
22 galaxies = input_space.each_with_index.flat_map {|row, y| row.each_with_index.map {|cell, x| [x, y] if cell == GALAXY}}.compact | |
23 galactic_distances = galaxies.combination(2).map do |a, b| | |
24 x_1, x_2 = [a[0], b[0]].minmax | |
25 y_1, y_2 = [a[1], b[1]].minmax | |
26 expanded_cols = ((x_1..x_2).to_a & open_columns).length | |
27 expanded_rows = ((y_1..y_2).to_a & open_rows).length | |
28 | |
29 # Avoid double-counting the expanded cell by subtracting the number of columns first rather any complex logic | |
30 x_2 - x_1 + - expanded_cols + (expanded_cols * EXPANSION_FACTOR) + y_2 - y_1 + - expanded_rows + (expanded_rows * EXPANSION_FACTOR) | |
31 end | |
32 puts galactic_distances.sum |