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to Two Bucket in the Ruby Track

Published at May 30 2019 · 0 comments
Instructions
Test suite
Solution

Given two buckets of different size, demonstrate how to measure an exact number of liters by strategically transferring liters of fluid between the buckets.

Since this mathematical problem is fairly subject to interpretation / individual approach, the tests have been written specifically to expect one overarching solution.

To help, the tests provide you with which bucket to fill first. That means, when starting with the larger bucket full, you are NOT allowed at any point to have the smaller bucket full and the larger bucket empty (aka, the opposite starting point); that would defeat the purpose of comparing both approaches!

Your program will take as input:

  • the size of bucket one
  • the size of bucket two
  • the desired number of liters to reach
  • which bucket to fill first, either bucket one or bucket two

Your program should determine:

  • the total number of "moves" it should take to reach the desired number of liters, including the first fill
  • which bucket should end up with the desired number of liters (let's say this is bucket A) - either bucket one or bucket two
  • how many liters are left in the other bucket (bucket B)

Note: any time a change is made to either or both buckets counts as one (1) move.

Example: Bucket one can hold up to 7 liters, and bucket two can hold up to 11 liters. Let's say bucket one, at a given step, is holding 7 liters, and bucket two is holding 8 liters (7,8). If you empty bucket one and make no change to bucket two, leaving you with 0 liters and 8 liters respectively (0,8), that counts as one "move". Instead, if you had poured from bucket one into bucket two until bucket two was full, leaving you with 4 liters in bucket one and 11 liters in bucket two (4,11), that would count as only one "move" as well.

To conclude, the only valid moves are:

  • pouring from one bucket to another
  • emptying one bucket and doing nothing to the other
  • filling one bucket and doing nothing to the other

Written with <3 at Fullstack Academy by Lindsay Levine.


For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby two_bucket_test.rb

To include color from the command line:

ruby -r minitest/pride two_bucket_test.rb

Source

Water Pouring Problem http://demonstrations.wolfram.com/WaterPouringProblem/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

two_bucket_test.rb

require 'minitest/autorun'
require_relative 'two_bucket'

# Common test data version: 1.4.0 edbc86b
class TwoBucketTest < Minitest::Test
  def test_bucket_one_size_3_bucket_two_size_5_goal_1_start_with_bucket_one
    # skip
    subject = TwoBucket.new(3, 5, 1, 'one')
    assert_equal 4, subject.moves
    assert_equal 'one', subject.goal_bucket
    assert_equal 5, subject.other_bucket
  end

  def test_bucket_one_size_3_bucket_two_size_5_goal_1_start_with_bucket_two
    skip
    subject = TwoBucket.new(3, 5, 1, 'two')
    assert_equal 8, subject.moves
    assert_equal 'two', subject.goal_bucket
    assert_equal 3, subject.other_bucket
  end

  def test_bucket_one_size_7_bucket_two_size_11_goal_2_start_with_bucket_one
    skip
    subject = TwoBucket.new(7, 11, 2, 'one')
    assert_equal 14, subject.moves
    assert_equal 'one', subject.goal_bucket
    assert_equal 11, subject.other_bucket
  end

  def test_bucket_one_size_7_bucket_two_size_11_goal_2_start_with_bucket_two
    skip
    subject = TwoBucket.new(7, 11, 2, 'two')
    assert_equal 18, subject.moves
    assert_equal 'two', subject.goal_bucket
    assert_equal 7, subject.other_bucket
  end

  def test_bucket_one_size_1_bucket_two_size_3_goal_3_start_with_bucket_two
    skip
    subject = TwoBucket.new(1, 3, 3, 'two')
    assert_equal 1, subject.moves
    assert_equal 'two', subject.goal_bucket
    assert_equal 0, subject.other_bucket
  end

  def test_bucket_one_size_2_bucket_two_size_3_goal_3_start_with_bucket_one
    skip
    subject = TwoBucket.new(2, 3, 3, 'one')
    assert_equal 2, subject.moves
    assert_equal 'two', subject.goal_bucket
    assert_equal 2, subject.other_bucket
  end
end
# frozen_string_literal: true

class TwoBucket
  class Bucket
    EMPTY = 0
    private_constant :EMPTY

    attr_reader :name, :capacity, :contents

    def initialize(name, capacity)
      @name = name
      @capacity = capacity
      @contents = EMPTY
    end

    def empty
      self.contents = EMPTY
    end

    def empty?
      contents == EMPTY
    end

    def fill
      self.contents = capacity
      self
    end

    def full?
      contents == capacity
    end

    def pour_fluid_into(other)
      amount = calculate_fluid_amount(other)
      other.contents += amount
      self.contents -= amount
    end

    protected

    attr_writer :contents

    private

    def calculate_fluid_amount(other)
      [other.capacity - other.contents, contents].min
    end
  end
  private_constant :Bucket

  ONE = "one"
  private_constant :ONE
  TWO = "two"
  private_constant :TWO

  attr_reader :goal_bucket, :moves, :other_bucket

  def initialize(capacity1, capacity2, goal, start_bucket)
    @goal = goal
    @goal_bucket, @other_bucket =
      [capacity1, capacity2, start_bucket]
      .then(&method(:initialize_buckets))
      .then(&method(:initialize_moves))
  end

  private

  attr_reader :goal
  attr_writer :moves

  def initialize_buckets((capacity1, capacity2, start_bucket))
    bucket_one = Bucket.new(ONE, capacity1)
    bucket_two = Bucket.new(TWO, capacity2)
    self.moves = 1
    if start_bucket == ONE
      [bucket_one.fill, bucket_two]
    else
      [bucket_two.fill, bucket_one]
    end
  end

  def initialize_moves((start_bucket, other_bucket))
    loop do
      return [start_bucket.name, other_bucket.contents] if
        start_bucket.contents == goal
      return [other_bucket.name, start_bucket.contents] if
        other_bucket.contents == goal

      transfer_fluid(start_bucket, other_bucket)
      self.moves += 1
    end
  end

  def transfer_fluid(start_bucket, other_bucket)
    if start_bucket.empty?
      start_bucket.fill
    elsif other_bucket.capacity == goal
      other_bucket.fill
    elsif other_bucket.full?
      other_bucket.empty
    else
      start_bucket.pour_fluid_into(other_bucket)
    end
  end
end

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