1 files changed, 69 insertions, 0 deletions
diff --git a/day12/part1.rb b/day12/part1.rb
new file mode 100644
index 0000000..cc58d7d
--- /dev/null
+++ b/day12/part1.rb
@@ -0,0 +1,69 @@
+class Node
+  def initialize(height)
+    @height = height
+    @neighbours = []
+    @visited = false
+    @distance = Float::INFINITY
+  end
+
+  attr_reader :height, :neighbours
+
+  attr_accessor :visited, :distance
+
+  def add_neighbour(node)
+    @neighbours << node
+  end
+end
+
+start = nil
+goal = nil
+
+grid = $stdin.readlines.map do |line|
+  line.strip.chars.map do |ch|
+    n = Node.new(
+      case ch
+      when ?a..?z
+        ch.ord - 96
+      when ?S
+        1
+      when ?E
+        26
+      end
+    )
+    start = n if ch == ?S
+    goal = n if ch == ?E
+    n
+  end
+end
+
+h = grid.length
+w = grid[0].length
+
+h.times.each do |rix|
+  w.times.each do |cix|
+    grid[rix][cix].add_neighbour(grid[rix-1][cix]) if rix - 1 >= 0
+    grid[rix][cix].add_neighbour(grid[rix][cix-1]) if cix - 1 >= 0
+    grid[rix][cix].add_neighbour(grid[rix+1][cix]) if rix + 1 < h
+    grid[rix][cix].add_neighbour(grid[rix][cix+1]) if cix + 1 < w
+  end
+end
+
+unvisited = grid.flatten
+start.distance = 0
+
+current = start
+
+until goal.visited
+  current.neighbours.select { |n|
+    !n.visited &&
+    (n.height - current.height) < 2
+  }.each { |n|
+    d = current.distance + 1
+    n.distance = d if d < n.distance
+  }
+  current.visited = true
+  unvisited.delete(current)
+  current = unvisited.min{|a, b| a.distance <=> b.distance}
+end
+
+puts goal.distance