Day 17 part 2 Ruby solution

Author: creideiki

17-2.rb

@@ -0,0 +1,254 @@
+#!/usr/bin/env ruby
+
+require 'numo/narray'
+
+class Rock
+  @@shapes = [
+    [[1, 1, 1, 1]],
+    [[0, 1, 0],
+     [1, 1, 1],
+     [0, 1, 0]],
+    [[0, 0, 1],
+     [0, 0, 1],
+     [1, 1, 1]],
+    [[1],
+     [1],
+     [1],
+     [1]],
+    [[1, 1],
+     [1, 1]]
+  ]
+
+  def self.shapes
+    @@shapes
+  end
+
+  def [](row, col)
+    @rock[row][col]
+  end
+
+  def width
+    @rock[0].size
+  end
+
+  def height
+    @rock.size
+  end
+
+  attr_accessor :x, :y
+
+  def initialize(shape)
+    @rock = @@shapes[shape]
+    @x = 2
+    @y = 0
+  end
+end
+
+class Cave
+  def initialize(jets)
+    @num_rocks = 0
+    @height = 25
+    @map = Numo::UInt8.zeros(@height, 7)
+    @next_shape = -1
+    @jets = jets.chars.map { |j| j == '<' ? -1 : +1 }
+    @jet_offset = -1
+    @rock = nil
+    @highest_rock = @height
+  end
+
+  attr_reader :num_rocks, :highest_rock
+
+  def find_repetition
+    base = @jets.size
+    1.upto(@jets.size * Rock.shapes.size) do |window_size|
+      maybe_repeats = true
+      window_size.times do |row|
+        7.times do |col|
+          if @map[@height - base - window_size * 0 - row, col] !=
+             @map[@height - base - window_size * 1 - row, col] or
+             @map[@height - base - window_size * 1 - row, col] !=
+             @map[@height - base - window_size * 2 - row, col]
+            maybe_repeats = false
+            break
+          end
+        end
+        break unless maybe_repeats
+      end
+      return [base, window_size] if maybe_repeats
+    end
+  end
+
+  def rock_height
+    @height - @highest_rock
+  end
+
+  def step!
+    unless @rock
+      @next_shape = (@next_shape + 1) % Rock.shapes.size
+      @rock = Rock.new(@next_shape)
+      @rock.y = @highest_rock - 3 - @rock.height
+      expand! if @rock.y.negative?
+    end
+    push!
+    @rock = nil unless fall!
+  end
+
+  def push!
+    @jet_offset = (@jet_offset + 1) % @jets.size
+    dir = @jets[@jet_offset]
+    can_move = true
+    if @rock.x + dir < 0 or
+       @rock.width + @rock.x + dir > 7
+      can_move = false
+    else
+      @rock.height.times do |row|
+        @rock.width.times do |col|
+          next unless @rock[row, col] == 1
+
+          if @map[row + @rock.y, col + @rock.x + dir] != 0
+            can_move = false
+            break
+          end
+        end
+      end
+    end
+    @rock.x += dir if can_move
+  end
+
+  def fall!
+    can_fall = true
+    if @rock.height + @rock.y >= @height
+      can_fall = false
+    else
+      @rock.height.times do |row|
+        @rock.width.times do |col|
+          next unless @rock[row, col] == 1
+
+          if @map[row + @rock.y + 1, col + @rock.x] != 0
+            can_fall = false
+            break
+          end
+        end
+      end
+    end
+    if can_fall
+      @rock.y += 1
+    else
+      @rock.height.times do |row|
+        @rock.width.times do |col|
+          @map[row + @rock.y, col + @rock.x] = @rock[row, col]
+        end
+      end
+      @highest_rock = [@rock.y, @highest_rock].min
+      @num_rocks += 1
+    end
+    can_fall
+  end
+
+  def expand!
+    add = 100
+    z = Numo::UInt8.zeros(add, 7)
+    @map = z.append(@map, axis:0)
+    @highest_rock += add
+    @rock.y += add if @rock
+    @height += add
+  end
+
+  def to_s
+    s = "<#{self.class}:\n"
+    s += "Next shape: #{@next_shape}, next push: #{@jets[@jet_offset]}\n"
+    s += "Highest rock: #{@highest_rock}\n"
+    @height.times do |row|
+      s += row.to_s.rjust(Math::log10(@height).ceil, '0') + ' '
+      7.times do |col|
+        tile = 0
+        if @rock and
+           row.between?(@rock.y, @rock.y + @rock.height - 1) and
+           col.between?(@rock.x, @rock.x + @rock.width - 1) and
+           @rock[row - @rock.y, col - @rock.x] == 1
+          tile = 2
+        end
+        tile += @map[row, col]
+        s += case tile
+             when 0
+               '.'
+             when 1
+               '#'
+             when 2
+               '@'
+             else
+               '!'
+             end
+      end
+      s += "\n"
+    end
+    if @rock
+      s += "Rock: x: #{@rock.x}, y: #{@rock.y}\n"
+      @rock.height.times do |row|
+        @rock.width.times do |col|
+          s += @rock[row, col].zero? ? '.' : '@'
+        end
+        s += "\n"
+      end
+      s += '>'
+    end
+    s
+  end
+
+  alias inspect to_s
+end
+
+input = File.read('17.input').strip
+
+# Caves will be filled as:
+#
+# Remaining
+# Period
+# Period
+# ...
+# Period
+# Period
+# Base
+
+# "cave" will be base + 3 periods, to find the repetition
+cave = Cave.new(input)
+
+until cave.rock_height >= input.size + input.size * Rock.shapes.size * 3 do
+  cave.step!
+end
+
+base, period_height = cave.find_repetition
+
+# "cave2" will be base + 1 period, to count the number of rocks in one
+# period
+cave2 = Cave.new(input)
+
+until cave2.rock_height >= base do
+  cave2.step!
+end
+
+base_rocks = cave2.num_rocks
+
+until cave2.rock_height >= base + period_height do
+  cave2.step!
+end
+
+period_rocks = cave2.num_rocks - base_rocks
+
+final_rock = 1_000_000_000_000
+periods = (final_rock - base_rocks) / period_rocks
+remaining_rocks = final_rock - base_rocks - periods * period_rocks
+
+remaining_rocks.times do
+  cave2.step!
+end
+
+# "cave3" will be base + remaining, to count the rocks outside of any
+# periods
+cave3 = Cave.new(input)
+
+until cave3.num_rocks == base_rocks + remaining_rocks do
+  cave3.step!
+end
+
+print periods * period_height + cave3.rock_height, "\n"