Published at Feb 19 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
```

```
class Bucket
attr_reader :size
attr_accessor :holding
def initialize(size, holding)
@size = size
@holding = holding
end
def fill!
@holding = @size
end
def empty!
@holding = 0
end
def full?
@holding == @size
end
def empty?
@holding == 0
end
def available
@size - @holding
end
end
class TwoBucket
attr_reader :bucket_one
attr_reader :bucket_two
attr_reader :liters
attr_reader :parent
def initialize(one_size, two_size, liters, first, one_holding: 0, two_holding: 0, parent: nil)
@parent = parent
@bucket_one = Bucket.new(one_size, one_holding)
@bucket_two = Bucket.new(two_size, two_holding)
@liters = liters
if first == 'one'
bucket_one.fill!
elsif first == 'two'
bucket_two.fill!
end
end
def to_s
holding_pair.to_s
end
def moves
if !@moves
final_state
end
@moves = final_state.parent_count
end
def parent_count
count = 0
state = self
until state.nil?
state = state.parent
count += 1
end
count
end
def final_state
@final_state ||= begin
seen = {}
ideal_states = []
children = [self]
while !children.empty?
child = children.pop
if child.holding_pair.include?(liters)
ideal_states << child
next
end
next if seen.has_key?(child.holding_pair)
seen[child.holding_pair] = true
operations = [
child.clone.pour_one_to_two,
child.clone.pour_two_to_one,
child.clone.fill_two,
child.clone.empty_one,
]
if !child.bucket_two.empty?
operations << child.clone.fill_one
end
if !child.bucket_one.full?
operations << child.clone.empty_two
end
operations.each do |sub|
next if sub.holding_pair == child.holding_pair
next if sub.holding_pair == [0, 0]
children << sub
end
end
ideal_states.min_by {|x| x.parent_count}
end
end
def holding_pair
[bucket_one.holding, bucket_two.holding]
end
def clone
TwoBucket.new(
bucket_one.size,
bucket_two.size, liters,
nil,
one_holding: bucket_one.holding,
two_holding: bucket_two.holding,
parent: self
)
end
def goal_bucket
final_state.bucket_one.holding == liters ? 'one' : 'two'
end
def other_bucket
if goal_bucket == 'one'
final_state.bucket_two.holding
else
final_state.bucket_one.holding
end
end
def empty_one
bucket_one.empty!
self
end
def empty_two
bucket_two.empty!
self
end
def fill_one
bucket_one.fill!
self
end
def fill_two
bucket_two.fill!
self
end
def pour_one_to_two
if bucket_one.holding < bucket_two.available
transfer = bucket_one.holding
else
transfer = bucket_two.available
end
bucket_two.holding += transfer
bucket_one.holding -= transfer
self
end
def pour_two_to_one
if bucket_two.holding < bucket_one.available
transfer = bucket_two.holding
else
transfer = bucket_one.available
end
bucket_one.holding += transfer
bucket_two.holding -= transfer
self
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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