Mercurial > repos > other > adventofcode2023
diff day11.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> |
|---|---|
| date | Mon, 11 Dec 2023 20:08:47 +0000 |
| parents | |
| children |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/day11.rb Mon Dec 11 20:08:47 2023 +0000 @@ -0,0 +1,26 @@ +#! /usr/bin/env ruby + +if ARGV.length != 1 + abort("Incorrect arguments - needs input file") +elsif not File.exist? (ARGV[0]) + abort("File #{ARGV[0]} did not exist") +end + +file = ARGV[0] + +OPEN_SPACE = "." +GALAXY = "#" + +input_space = File.open(file, "r").each_line(chomp: true).map(&:each_char).map(&:to_a) + +first, *rest = input_space +open_columns = first.zip(*rest).map {|col| col.all? {|cell| cell == OPEN_SPACE}} + +expanded_space = input_space.flat_map do |row| + new_row = row.zip(open_columns).flat_map {|cell, is_open| is_open ? [cell, cell] : [cell]} + if row.all? {|cell| cell == OPEN_SPACE} then [new_row, new_row] else [new_row] end +end + +galaxies = expanded_space.each_with_index.flat_map {|row, y| row.each_with_index.map {|cell, x| [x, y] if cell == GALAXY}}.compact +galactic_distances = galaxies.combination(2).map {|a, b| (a[0] - b[0]).abs + (a[1] - b[1]).abs} +puts galactic_distances.sum