marksim · December 15, 2013 06:13 · Dec 15, 2013
diff --git a/game_of_life.rb b/game_of_life.rb
@@ -0,0 +1,75 @@
+require 'rspec'
+
+class GameOfLife
+  def initialize(generation)
+    @generation = generation
+  end
+
+  attr_reader :generation
+
+  def is_alive?(x, y)
+    generation.include?([x, y])
+  end
+
+  def number_of_neighbors_for(x, y)
+    generation.select do |dx, dy|
+      (x-1..x+1).include?(dx) && (y-1..y+1).include?(dy)
+    end.count - (is_alive?(x, y) ? 1 : 0)
+  end
+
+  def should_regen?(x, y)
+    !generation.include?([x, y]) && number_of_neighbors_for(x, y) == 3
+  end
+
+  def regenerate_dead_neighbors(x, y)
+    (-4..4).map { |m| [x+m/3, y+m%3] if should_regen?(x+m/3, y+m%3) }.compact
+  end
+
+  def should_survive?(x, y)
+    [2, 3].include?(number_of_neighbors_for(x, y))
+  end
+
+  def tick
+    @generation = generation.map do |x, y|
+      regenerate_dead_neighbors(x, y) + (should_survive?(x, y) ? [[x, y]] : [])
+    end.flatten(1).uniq.sort
+  end
+end
+
+
+
+describe "Game of Life!!!" do
+  let(:game) { GameOfLife.new(board) }
+
+	context "Lonely" do
+    let(:board) { [[1, 1]] }
+		it "dies after one generation" do
+			game.tick
+			expect(game.generation).to be_empty
+		end
+	end
+
+	context "Continuing" do
+    let(:board) { [[0, 0], [0, 1], [1, 0], [1, 1], [2, 2], [2, 3], [3, 2], [3, 3]] } # Beacon
+		it "knows how many neighbors" do
+			expect(game.number_of_neighbors_for(1, 1)).to eql 4
+		end
+
+		it "2 die after one generation" do
+			game.tick
+			expect(game.generation).to eql [[0, 0], [0, 1], [1, 0], [2, 3], [3, 2], [3, 3]]
+		end
+	end
+
+	context "Regenerate" do
+    let(:board) { [[0, 0], [0, 1], [1, 0], [2, 3], [3, 2], [3, 3]] }
+		it "knows how many neighbors" do
+			expect(game.number_of_neighbors_for(1, 1)).to eql 3
+		end
+
+		it "regenerates after one generation with exactly 3 neighbors" do
+			game.tick
+			expect(game.generation).to eql [[0, 0], [0, 1], [1, 0], [1, 1], [2, 2], [2, 3], [3, 2], [3, 3]].sort
+		end
+	end
+end
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