Day 10 part 1 Ruby solution

Author: creideiki

10-1.rb

@@ -0,0 +1,82 @@
+#!/usr/bin/env ruby
+
+input = File.read('10.input').lines.map(&:strip).map(&:chars)
+height = input.size
+width = input[0].size
+
+distances = Array.new height
+distances = distances.map { |_| Array.new(width, -1) }
+
+pipes = Array.new height
+pipes = pipes.map { |_| Array.new width }
+
+start_y = -1
+start_x = -1
+height.times do |y|
+  width.times do |x|
+    pipes[y][x] = case input[y][x]
+                  when 'S'
+                    distances[y][x] = 0
+                    start_y = y
+                    start_x = x
+                    []
+                  when '.'
+                    []
+                  when '|'
+                    [:north, :south]
+                  when '-'
+                    [:east, :west]
+                  when 'L'
+                    [:north, :east]
+                  when 'J'
+                    [:north, :west]
+                  when '7'
+                    [:south, :west]
+                  when 'F'
+                    [:south, :east]
+                  end
+  end
+end
+
+if start_y >= 1 and pipes[start_y - 1][start_x].include? :south
+  pipes[start_y][start_x] << :north
+end
+if start_y < height - 1 and pipes[start_y + 1][start_x].include? :north
+  pipes[start_y][start_x] << :south
+end
+if start_x >= 1 and pipes[start_y][start_x - 1].include? :east
+  pipes[start_y][start_x] << :west
+end
+if start_x < width - 1 and pipes[start_y][start_x + 1].include? :west
+  pipes[start_y][start_x] << :east
+end
+
+cur_dist = -1
+cur_y = start_y
+cur_x = start_x
+from = nil
+
+loop do
+  cur_dist = distances[cur_y][cur_x]
+  if from != :north and cur_y > 0 and pipes[cur_y][cur_x].include? :north and pipes[cur_y - 1][cur_x].include? :south
+    distances[cur_y - 1][cur_x] = cur_dist + 1 unless distances[cur_y - 1][cur_x] == 0
+    from = :south
+    cur_y -= 1
+  elsif from != :east and cur_x < width - 1 and pipes[cur_y][cur_x].include? :east and pipes[cur_y][cur_x + 1].include? :west
+    distances[cur_y][cur_x + 1] = cur_dist + 1 unless distances[cur_y - 1][cur_x] == 0
+    from = :west
+    cur_x += 1
+  elsif from != :south and cur_y < height - 1 and pipes[cur_y][cur_x].include? :south and pipes[cur_y + 1][cur_x].include? :north
+    distances[cur_y + 1][cur_x] = cur_dist + 1 unless distances[cur_y - 1][cur_x] == 0
+    from = :north
+    cur_y += 1
+  elsif from != :west and cur_x > 0 and pipes[cur_y][cur_x].include? :west and pipes[cur_y][cur_x - 1].include? :east
+    distances[cur_y][cur_x - 1] = cur_dist + 1 unless distances[cur_y - 1][cur_x] == 0
+    from = :east
+    cur_x -= 1
+  end
+
+  break if cur_y == start_y and cur_x == start_x
+end
+
+print (cur_dist + 1) / 2, "\n"