A template for containing puzzle problems in a single file, including input data, and tests.

sock_market.rb

# frozen_string_literal: true

# The Sock Merchant
# from https://www.hackerrank.com/challenges/sock-merchant/problem
#
# Run the solver with the input after __END__
# $ ruby sock_merchant.rb
#
# Run the solver using a file as input
# $ ruby sock_merchant.rb test_input.txt
#
# Run solver specs with
# $ ruby sock_merchant.rb --specs

require "bundler/inline"

# Uncomment this block to install byebug
# gemfile true do
#   source "https://rubygems.org"

#   gem "test-unit"

#   # Useful for debugging
#   gem "byebug", platforms: [:mri, :mingw, :x64_mingw]
#   gem "pry-byebug"
# end

require 'test/unit'
Test::Unit::AutoRunner.need_auto_run = false

class SockCounter
  def initialize(socks)
    @socks = socks
  end

  def pair_count
    # group by type
    # binding.pry
    count_per_type = @socks.group_by(&:itself)
    pairs_per_type = count_per_type.transform_values { |v| v.size.div 2 }
    total_pairs = pairs_per_type.values.sum
    total_pairs
  end
end

class SockCounterSpec < Test::Unit::TestCase
  def expect_pair_count(expected_pair_count, socks:)
    pair_count = SockCounter.new(socks).pair_count
    assert_equal expected_pair_count, pair_count
  end

  def test_none
    expect_pair_count(0, socks: [])
  end

  def test_no_pairs
    expect_pair_count(0, socks: [1, 2, 3, 4])
  end

  def test_some_pairs
    expect_pair_count(2, socks: [1, 2, 3, 4, 1, 2])
  end
end

if $PROGRAM_NAME == __FILE__
  first_argument = ARGV.shift

  if first_argument == '--specs'
    # Run the specs
    Test::Unit::AutoRunner.need_auto_run = true
  else
    data_source = first_argument.nil? ? DATA.read : File.read(first_argument)
    # Run the solver
    raw_number_of_socks, raw_socks = data_source.split(/\r?\n/, 2)

    number_of_socks = raw_number_of_socks.to_i
    socks = raw_socks.split(' ').map(&:to_i)

    if number_of_socks != socks.size
      raise("Sock mismatch! Expected #{number_of_socks}, got #{socks.size}")
    end

    pairs = SockCounter.new(socks).pair_count
    puts pairs
  end
end

__END__
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