Published at May 30 2019
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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
```

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

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

```
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
```

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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