class Array
  def binary_search(val, low=0, high=(length - 1))
    return nil if high < low
    mid = (low + high) >> 1
    case val <=> self[mid]
      when -1
        binary_search(val, low, mid - 1)
      when 1
        binary_search(val, mid + 1, high)
      else mid
    end
  end
end

ary = [0,1,4,5,6,7,8,9,12,26,45,67,78,90,98,123,211,234,456,769,865,2345,3215,14345,24324]

[0,42,45,24324,99999].each do |val|
  i = ary.binary_search(val)
  if i
    puts "found #{val} at index #{i}: #{ary[i]}"
  else
    puts "#{val} not found in array"
  end
end