2023: Day 11, part 1

2023/day11.rb

@@ -0,0 +1,42 @@
+input = ARGF.read.strip
+by_row = input.lines.map(&:rstrip).map { |line| line.split("") }
+
+def needs_expand(data)
+  expand = []
+  data.each_with_index { |row, i| expand << i if row.all? { |c| c == "." } }
+  expand
+end
+
+def print_cosmos(cosmos)
+  cosmos.each do |line|
+    puts line.join("")
+  end
+end
+
+# do expansion
+row_expand = needs_expand(by_row)
+row_expand.reverse.each do |i|
+  by_row.insert(i, by_row[i].dup)
+end
+
+by_column = by_row.transpose
+col_expand = needs_expand(by_column)
+col_expand.reverse.each do |i|
+  by_column.insert(i, by_column[i].dup)
+end
+
+cosmos = by_column.transpose
+
+# find galaxies
+galaxies = []
+(0...cosmos.first.length).each do |x|
+  (0...cosmos.length).each do |y|
+    galaxies << [x, y] if cosmos[y][x] == "#"
+  end
+end
+
+def galaxy_distance(a, b)
+  (a[0] - b[0]).abs + (a[1] - b[1]).abs
+end
+
+puts "Part 1: #{galaxies.combination(2).map { |a, b| galaxy_distance(a, b) }.sum}"

2023/input/day11.sample

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+...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....
+

2023/input/day11.txt

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