Programming Elixir exercise 6 in modules and functions chapter

modules-and-functions-6.exs

# Prompt directly from book:

# Exercise: ModulesAndFunctions-6
# I’m thinking of a number between 1 and 1000.…

# The most efficient way to find the number is to guess halfway between the low and high numbers of the range. If our guess is too big, then the answer lies between the bottom of the range and one less than our guess. If our guess is too small, then the answer lies between one more than our guess and the end of the range.

# Your API will be guess(actual, range), where range is an Elixir range. Your output should look similar to this:

# ​ 	iex> Chop.guess(273, 1..1000)
# ​ 	Is it 500
# ​ 	Is it 250
# ​ 	Is it 375
# ​ 	Is it 312
# ​ 	Is it 281
# ​ 	Is it 265
# ​ 	Is it 273
# ​ 	273

# Hints:

# You may need to implement helper functions with an additional parameter (the currently guessed number).

# The div(a,b) function performs integer division.

# Guard clauses are your friends.

# Patterns can match the low and high parts of a range (a..b=4..8).



defmodule Chop do
  def guess(actual, a..b = range, guess) when guess > actual do
    IO.puts("Is it #{guess}")
    guess(actual, a..guess, midpoint(range))
  end

  def guess(actual, a..b = range, guess) when guess < actual do
    IO.puts("Is it #{guess}")
    guess(actual, guess..b, midpoint(range))
  end

  def guess(actual, a..b = range, guess) when guess == actual do
    IO.puts("#{guess}")
  end

  def guess(actual, a..b = range) when is_integer(actual) and is_map(range) do
    guess(actual, range, midpoint(range))
  end

  def range_midpoint_index(range) do
    list = Enum.to_list(range)
    div(length(list) - 1, 2)
  end

  def midpoint(range) do
    Enum.at(range, range_midpoint_index(range))
  end
end

IO.puts Servy.Guess.guess(273, 1..1000)

# Output:
# Is it 500
# Is it 500
# Is it 250
# Is it 250
# Is it 375
# Is it 375
# Is it 312
# Is it 312
# Is it 281
# Is it 281
# Is it 265
# Is it 265
# 273
# ok
# [Chop]