integer_guesser.exs

# IntegerGuesser.guess(number, range)
# Conducts a binary serach within the range for the integer and
# reports its path along the way.
#
# EX:
#  iex(1)> IntegerGuesser.guess(273, 1..1000)
#  Is it 500?... Nope
#  Is it 249?... Nope
#  Is it 375?... Nope
#  Is it 311?... Nope
#  Is it 279?... Nope
#  Is it 263?... Nope
#  Is it 271?... Nope
#  Is it 275?... Nope
#  Is it 272?... Nope
#  Is it 274?... Nope
#  Is it 272?... Nope
#  "It's 273!"

defmodule IntegerGuesser do

  def guess(actual, first..last)
  when actual in first..last do
    next_guess(actual, div(last, 2), first..last)
  end

  defp next_guess(actual, guess, _)
  when guess == actual do
    "It's #{guess}!"
  end

  defp next_guess(actual, guess, first..last)
  when guess < actual do
    report_guess(guess)
    next_guess(actual, div(last+guess, 2)+1, guess+1..last)
  end

  defp next_guess(actual, guess, first..last)
  when guess > actual do
    report_guess(guess)
    next_guess(actual, div(guess+first, 2)-1, first..guess-1)
  end

  defp report_guess(guess) do
    IO.puts("Is it #{guess}?... Nope")
  end
end