Add solution to day 6.

day6.cr

@@ -0,0 +1,65 @@
+require "./common.cr"
+
+lines = File.read("day6_input").split("\n")
+lines.pop
+
+REGEX = /(\d+), (\d+)/
+coords = lines.map(&.match(REGEX))
+  .select { |it| it != nil }
+  .map { |match| { match.not_nil![1].to_i32, match.not_nil![2].to_i32 } }
+
+def distance(a, b)
+  (a[0] - b[0]).abs + (a[1] - b[1]).abs
+end
+
+def compute_area(coords, coord)
+  visited = Set(Tuple(Int32, Int32)).new
+  total = 0
+
+  coord_queue = Set(Tuple(Int32, Int32)).new
+  coord_queue << coord
+
+  while !coord_queue.empty?
+    new_coord = coord_queue.first
+    coord_queue.delete new_coord
+
+    next if visited.includes? new_coord
+    visited << new_coord
+
+    distances = coords.group_by do |coord|
+      distance(coord, new_coord)
+    end
+    min_distance = distances.keys.min
+
+    next if distances[min_distance].size != 1
+    next if distances[min_distance][0] != coord
+
+    total += 1
+    x, y = new_coord
+    coord_queue << { x + 1, y }
+    coord_queue << { x - 1, y }
+    coord_queue << { x, y + 1 }
+    coord_queue << { x, y - 1 }
+
+    if total > 10000
+      return 0
+    end
+  end
+
+  return total
+end
+
+def find_region(coords)
+  total = 0
+  (-11000/2..11000/2).each do |x|
+    (-11000/2..11000/2).each do |y|
+      coord = {x, y}
+      total += 1 if coords.sum { |it| distance(it, coord) } < 10000
+    end
+  end
+  
+  return total
+end
+
+puts coords.max_of { |it| compute_area(coords, it) }
+puts find_region(coords)