--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/day11b.rb	Mon Dec 11 20:08:47 2023 +0000
@@ -0,0 +1,32 @@
+#! /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 = "#"
+EXPANSION_FACTOR = 1000000
+
+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).each_with_index.map {|col, idx| col.all? {|cell| cell == OPEN_SPACE} ? idx : nil}.compact
+open_rows = input_space.each_with_index.map {|row, idx| row.all? {|cell| cell == OPEN_SPACE} ? idx : nil}.compact
+
+
+galaxies = input_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 do |a, b|
+	x_1, x_2 = [a[0], b[0]].minmax
+	y_1, y_2 = [a[1], b[1]].minmax
+	expanded_cols = ((x_1..x_2).to_a & open_columns).length
+	expanded_rows = ((y_1..y_2).to_a & open_rows).length
+
+	# Avoid double-counting the expanded cell by subtracting the number of columns first rather any complex logic
+	x_2 - x_1 + - expanded_cols + (expanded_cols * EXPANSION_FACTOR) + y_2 - y_1 + - expanded_rows + (expanded_rows * EXPANSION_FACTOR)
+end
+puts galactic_distances.sum