100 doors by ruby

gistfile1.rb

# 安直にやる
doors1 = (1..100).inject([false] * 100) {|a,p|
  a.each_with_index.map {|st,i| (i+1) % p == 0 ? !st : st }
}.map {|b| b ? :open : :close }

# 平方数だけが最終的 open になる、という性質を使う
doors2 = (1..100).map {|i|
  root = Math.sqrt(i)
  root == root.to_i ? :open : :close
}

# >> doors1
# => [:open, :close, :close, :open, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :open, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :close, :open]
# >> doors1 == doors2
# => true