cool tricks in ruby

tricks.rb

# Very fast way to determine if a string contains all unique characters
# Space O(1), Time O(N)
# Assumes ASCII strings. Unicode would require space of Array.new(1,111,998).
def is_unique(str)
  return false if str.length > 256
  chars = Array.new(256)
  str.each_byte.lazy.each do |c|
    return false if chars[c]
    chars[c] = true
  end
  true
end