Programming Elixir Exercises

modules-and-functions-4-and-5.exs

defmodule Mod do
  def sum(0), do: 0
  def sum(n), do: n + sum(n - 1)

  def gcd(x, 0), do: x
  def gcd(x, y), do: gcd(y, rem(x, y))
end

modules-and-functions-6.exs

defmodule Chop do
  # base case: if g equals actual then return g
  def guess(actual, _, g) when actual == g, do: g

  # when guess is too high, slice range in half by lower bounds
  def guess(actual, rng, g) when g > actual do
    lower.._ = rng
    guess actual, lower..midpoint(rng)
  end

  # when guess is too low, slice range in half by upper bounds
  def guess(actual, rng, g) when g < actual do
    _..upper = rng
    guess actual, midpoint(rng)..upper
  end

  # make guess
  def guess(actual, rng) do
    g = midpoint rng
    IO.puts "Guessing #{g}"
    guess actual, rng, g
  end

  # find midpoint of a range
  def midpoint(first..last), do: div (first + last), 2
end