Day 4: Bingo!

Not super happy with the until and while loops, but they're relatively
clean so calling it good enough for today.

2021/04/bingo.rb

@@ -0,0 +1,57 @@
+class Bingo
+  class Board
+    attr_reader :rows
+
+    def initialize(rows)
+      @rows = rows.map{_1.split.map(&:to_i)}
+      @columns = @rows.transpose
+    end
+
+    def won?(seen)
+      [*@rows, *@columns].any?{(_1 - seen).empty?}
+    end
+  end
+
+  def initialize(input)
+    @numbers = input[0].split(",").map(&:to_i)
+    @boards = input[1..-1].each_slice(6).map do |slice|
+      Board.new(slice[1..-1])
+    end
+  end
+
+  def winning_score
+    final_score(winning_board)
+  end
+
+  def losing_score
+    final_score(losing_board)
+  end
+
+  private
+
+  def final_score(board)
+    (board.rows.flatten - seen).sum * seen.last
+  end
+
+  def seen
+    @numbers[0..@last_called]
+  end
+
+  def winning_board
+    @last_called = 0
+    @last_called += 1 until (winning = @boards.find{_1.won?(seen)})
+    winning
+  end
+
+  def losing_board
+    @last_called = 0
+    boards = @boards.dup
+    while boards.length > 1
+      boards.reject!{_1.won?(seen)}
+      @last_called += 1
+    end
+    losing = boards.first
+    @last_called += 1 until losing.won?(seen)
+    losing
+  end
+end