Day 17 part 2

examples/17_b.txt

@@ -0,0 +1,5 @@
+111111111111
+999999999991
+999999999991
+999999999991
+999999999991

lib/days/17.rb

@@ -2,6 +2,11 @@ class Day17
   require 'fc'
   include Util
 
+  RIGHT = :right
+  LEFT = :left
+  DOWN = :down
+  UP = :up
+
   Crucible = Struct.new(
     :x, :y, :cost, :dir, :moves_in_dir
   ) do
@@ -16,7 +21,7 @@ def part1(input)
     goal = [grid.length - 1, grid.first.length - 1]
 
     queue = FastContainers::PriorityQueue.new(:min)
-    queue.push(Crucible.new(0, 0, 0, :down, 0), 0)
+    queue.push(Crucible.new(0, 0, 0, nil, 0), 0)
     visited = Set.new
 
     loop do
@@ -39,11 +44,6 @@ def part1(input)
     end
   end
 
-  LEFT_TO_RIGHT = :right
-  RIGHT_TO_LEFT = :left
-  DOWN = :down
-  UP = :up
-
   def available_moves(grid, position, current_cost, current_direction, num_direction)
     moves = []
 
@@ -72,34 +72,117 @@ def available_moves(grid, position, current_cost, current_direction, num_directi
     end
 
     if position[0] != grid.length - 1 &&
-       current_direction != RIGHT_TO_LEFT &&
-       !(current_direction == LEFT_TO_RIGHT && num_direction >= 3)
+       current_direction != LEFT &&
+       !(current_direction == RIGHT && num_direction >= 3)
 
       moves << Crucible.new(
         position[0] + 1,
         position[1],
         current_cost + grid[position[0] + 1][position[1]],
-        LEFT_TO_RIGHT,
-        current_direction == LEFT_TO_RIGHT ? num_direction + 1 : 1)
+        RIGHT,
+        current_direction == RIGHT ? num_direction + 1 : 1)
     end
 
     if !position[0].zero? &&
-       current_direction != LEFT_TO_RIGHT &&
-       !(current_direction == RIGHT_TO_LEFT && num_direction >= 3)
+       current_direction != RIGHT &&
+       !(current_direction == LEFT && num_direction >= 3)
 
       moves << Crucible.new(
         position[0] - 1,
         position[1],
         current_cost + grid[position[0] - 1][position[1]],
-        RIGHT_TO_LEFT,
-        current_direction == RIGHT_TO_LEFT ? num_direction + 1 : 1)
+        LEFT,
+        current_direction == LEFT ? num_direction + 1 : 1)
     end
 
     moves
   end
 
-  def part2(_input)
-    'TODO'
+  def part2(input)
+    grid = parse_grid(input, :to_i)
+    goal = [grid.length - 1, grid.first.length - 1]
+
+    queue = FastContainers::PriorityQueue.new(:min)
+    queue.push(Crucible.new(0, 0, 0, nil, 0), 0)
+
+    visited = Set.new
+
+    loop do
+      crucible = queue.top
+      queue.pop
+
+      return crucible.cost if crucible.pos == goal && crucible.moves_in_dir >= 4
+
+      next_steps = available_moves_v2(grid, crucible.pos, crucible.cost, crucible.dir, crucible.moves_in_dir)
+
+      next_steps.each do |next_step|
+        hash = [next_step.pos, next_step.dir, next_step.moves_in_dir]
+        next if visited.include?(hash)
+
+        visited.add(hash)
+        queue.push(next_step, next_step.cost)
+      end
+
+      break if queue.none?
+    end
+  end
+
+  def available_moves_v2(grid, position, current_cost, current_direction, num_direction)
+    moves = []
+
+    if position[1] != grid.first.length - 1 &&
+       current_direction != UP &&
+       !([RIGHT, LEFT].include?(current_direction) && num_direction < 4) &&
+       !(current_direction == DOWN && num_direction >= 10)
+
+      moves << Crucible.new(
+        position[0],
+        position[1] + 1,
+        current_cost + grid[position[0]][position[1] + 1],
+        DOWN,
+        current_direction == DOWN ? num_direction + 1 : 1)
+    end
+
+    if !position[1].zero? &&
+       current_direction != DOWN &&
+       !([RIGHT, LEFT].include?(current_direction) && num_direction < 4) &&
+       !(current_direction == UP && num_direction >= 10)
+
+      moves << Crucible.new(
+        position[0],
+        position[1] - 1,
+        current_cost + grid[position[0]][position[1] - 1],
+        UP,
+        current_direction == UP ? num_direction + 1 : 1)
+    end
+
+    if position[0] != grid.length - 1 &&
+       current_direction != LEFT &&
+       !([UP, DOWN].include?(current_direction) && num_direction < 4) &&
+       !(current_direction == RIGHT && num_direction >= 10)
+
+      moves << Crucible.new(
+        position[0] + 1,
+        position[1],
+        current_cost + grid[position[0] + 1][position[1]],
+        RIGHT,
+        current_direction == RIGHT ? num_direction + 1 : 1)
+    end
+
+    if !position[0].zero? &&
+       current_direction != RIGHT &&
+       !([UP, DOWN].include?(current_direction) && num_direction < 4) &&
+       !(current_direction == LEFT && num_direction >= 10)
+
+      moves << Crucible.new(
+        position[0] - 1,
+        position[1],
+        current_cost + grid[position[0] - 1][position[1]],
+        LEFT,
+        current_direction == LEFT ? num_direction + 1 : 1)
+    end
+
+    moves
   end
 
 end

test/17_test.rb

@@ -5,6 +5,7 @@
 class TestDay17 < Minitest::Test
   def setup
     @data = File.read(File.join(APP_ROOT, 'examples', '17.txt')).rstrip
+    @data_b = File.read(File.join(APP_ROOT, 'examples', '17_b.txt')).rstrip
     @day = Day17.new
   end
 
@@ -13,6 +14,7 @@ def test_part1
   end
 
   def test_part2
-    assert_equal @day.part2(@data), ''
+    assert_equal @day.part2(@data_b), 71
+    assert_equal @day.part2(@data), 94
   end
 end