16 part 2

lib/days/16.rb

@@ -26,11 +26,31 @@ def pos
 
   def part1(input)
     grid = parse_grid(input)
-    visited = Set.new
 
-    beams = [
-      Beam.new(0, 0, :right)
-    ]
+    solve(grid, Beam.new(0, 0, :right))
+  end
+
+  def part2(input)
+    grid = parse_grid(input)
+
+    values = []
+
+    grid.length.times do |x|
+      values << solve(grid, Beam.new(x, 0, :down))
+      values << solve(grid, Beam.new(x, grid.first.length - 1, :up))
+    end
+
+    grid.first.length.times do |y|
+      values << solve(grid, Beam.new(0, y, :right))
+      values << solve(grid, Beam.new(grid.length - 1, y, :right))
+    end
+
+    values.max
+  end
+
+  def solve(grid, initial)
+    visited = Set.new
+    beams = [initial]
 
     loop do
       new_beams = []
@@ -39,12 +59,11 @@ def part1(input)
         if beam.x.negative? ||
            beam.x >= grid.length ||
            beam.y.negative? ||
-           beam.y >= grid.first.length
+           beam.y >= grid.first.length ||
+           visited.include?(beam)
           next
         end
 
-        next if visited.include?(beam)
-
         visited.add(beam)
 
         case grid[beam.x][beam.y]
@@ -97,8 +116,4 @@ def part1(input)
     visited.map(&:pos).uniq.length
   end
 
-  def part2(input)
-    'TODO'
-  end
-
 end

test/16_test.rb

@@ -13,6 +13,6 @@ def test_part1
   end
 
   def test_part2
-    assert_equal @day.part2(@data), ''
+    assert_equal @day.part2(@data), 51
   end
 end