store_credit.rb

class TestCase
  def initialize(credit, item_prices)
    @credit           = credit
    @item_prices      = item_prices
    @number_of_items  = @item_prices.length
    @current_index    = 0
  end

  def iterate_and_test_and_return_winner

    return nil if (@current_index + 1) == @number_of_items

    found_match = false

    ( (@current_index + 1)...(@number_of_items) ).each do |candidate_index|
      if (test_starting_and_candidate_index(@current_index, candidate_index) )
        found_match = true
        return  [
                  {:index => @current_index,    :position_in_prices => @current_index   + 1, :price => @item_prices[@current_index]},
                  {:index => candidate_index,  :position_in_prices  => candidate_index + 1,  :price => @item_prices[candidate_index]}
                ]
      end
    end
    if (!found_match)
      @current_index += 1
      iterate_and_test_and_return_winner
    end

  end

  private

  def test_starting_and_candidate_index(current_index, candidate_index)
    @credit == @item_prices[current_index] + @item_prices[candidate_index]
  end

end

class StoreCreditInputFileParser
  def initialize(file_to_parse)
    @file_to_parse = File.open(file_to_parse, "r")
    @number_of_test_cases = @file_to_parse.readline.to_i
  end

  def generate_test_cases
    test_cases = []
    (1 .. @number_of_test_cases).each do |test_case_number|
      credit            = @file_to_parse.readline.to_i
      number_of_prices  = @file_to_parse.readline
      prices            = @file_to_parse.readline.split(' ').map(&:to_i)

      test_cases << TestCase.new(credit, prices)
    end
    @file_to_parse.close

    test_cases
  end

end

class StoreCreditTestRunner
  def initialize(input_hash)
    @print_mode = input_hash[:print_mode] || "submission"
    @test_cases = parse_input_hash(input_hash)
  end

  def run
    @test_cases.each_with_index do |test_case, index|
      test_case_result = test_case.iterate_and_test_and_return_winner
      print_result(index, test_case_result)
    end
  end

  private

  def parse_input_hash(input_hash)
    if ( input_hash[:file] )
      StoreCreditInputFileParser.new(input_hash[:file]).generate_test_cases
    elsif ( input_hash[:test_cases] )
      input_hash[:test_cases]
    else
      "INVALID INPUT"
    end
  end

  def print_result(test_case_index, test_case_result)
    if (!test_case_result)
      puts case_separator
      puts "Case ##{test_case_index}: No valid pair of items found"
      return
    end

    if ( @print_mode == "submission" )
      puts "Case ##{test_case_index + 1}: #{test_case_result[0][:position_in_prices]} #{test_case_result[1][:position_in_prices]}"
    else
      puts case_separator
      puts "Winning Positions:  #{test_case_result[0][:position_in_prices]}, #{test_case_result[1][:position_in_prices]}"
      puts "Winning Prices:     #{test_case_result[0][:price]}, #{test_case_result[1][:price]}"
      puts "Winning Indicies:   #{test_case_result[0][:index]}, #{test_case_result[1][:index]}"
    end
  end

  def case_separator
    "================================================="
  end

end

StoreCreditTestRunner.new({:file => "test_files/A-small-practice.in"}).run
StoreCreditTestRunner.new({:test_cases => [ TestCase.new(8, [4,4,0]) ], :print_mode => "debug"} ).run
StoreCreditTestRunner.new({:test_cases => [ TestCase.new(8, [4,4,0]), TestCase.new(2, [1,0,1]) ], :print_mode => "debug"} ).run
StoreCreditTestRunner.new({:test_cases => [ TestCase.new(8, [4,2,0]) ], :print_mode => "debug"} ).run