2016: Add day 1 part 2

2016/.rubocop.yml

@@ -0,0 +1,2 @@
+Metrics:
+  Enabled: false

2016/test/day01_test.rb

@@ -30,6 +30,8 @@ def self.turn_left(direction)
   end
 end
 
+Step = Data.define(:direction, :position)
+
 describe 'day01' do
   it 'solves part 01' do
     steps = Util.read_input('day01-input.txt').first.split(', ')
@@ -41,17 +43,57 @@ def self.turn_left(direction)
         when 'L'then Directions.turn_left(acc[0])
         else raise('invalid value')
         end
+      step_count = it[1..].to_i
 
-      step_numbers = it[1..].to_i
       case direction
-      when Directions::NORTH then [direction, [acc[1][0] + step_numbers, acc[1][1]]]
-      when Directions::EAST then [direction, [acc[1][0], acc[1][1] + step_numbers]]
-      when Directions::SOUTH then [direction, [acc[1][0] - step_numbers, acc[1][1]]]
-      when Directions::WEST then [direction, [acc[1][0], acc[1][1] - step_numbers]]
+      when Directions::NORTH then [direction, [acc[1][0] + step_count, acc[1][1]]]
+      when Directions::EAST then [direction, [acc[1][0], acc[1][1] + step_count]]
+      when Directions::SOUTH then [direction, [acc[1][0] - step_count, acc[1][1]]]
+      when Directions::WEST then [direction, [acc[1][0], acc[1][1] - step_count]]
       else raise('invalid value')
       end
     end
 
     assert_equal 279, result[1][0] + result[1][1]
   end
+
+  it 'solves part 02' do
+    steps = Util.read_input('day01-input.txt').first.split(', ')
+
+    path = steps.reduce [Step.new(Directions::NORTH, [0, 0])] do |acc, it|
+      prev = acc.last
+      direction =
+        case it[0]
+        when 'R' then Directions.turn_right(prev.direction)
+        when 'L'then Directions.turn_left(prev.direction)
+        else raise('invalid value')
+        end
+      step_count = it[1..].to_i
+
+      case direction
+      when Directions::NORTH
+        acc + (prev.position[0] + 1..prev.position[0] + step_count).map do |p|
+          Step.new(direction, [p, prev.position[1]])
+        end
+      when Directions::EAST
+        acc + (prev.position[1] + 1..prev.position[1] + step_count).map do |p|
+          Step.new(direction, [prev.position[0], p])
+        end
+      when Directions::SOUTH
+        acc + (prev.position[0] - 1..prev.position[0] - step_count).step(-1).map do |p|
+          Step.new(direction, [p, prev.position[1]])
+        end
+      when Directions::WEST
+        acc + (prev.position[1] - 1..prev.position[1] - step_count).step(-1).map do |p|
+          Step.new(direction, [prev.position[0], p])
+        end
+      else raise('invalid value')
+      end
+    end
+
+    positions = path.map(&:position)
+    duplicated = positions.detect { |p| positions.count(p) > 1 }
+
+    assert_equal 163, duplicated[0] + duplicated[1]
+  end
 end