Merge pull request #695 from adimasuhid/features/implement-change-exe…

…rcise

change: Implement Change exercise

config.json

@@ -872,6 +872,19 @@
         "Strings"
       ]
     },
+    {
+      "uuid": "dc6c3e44-1027-4d53-9653-ba06824f8bcf",
+      "slug": "change",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 5,
+      "topics": [
+        "Algorithms",
+        "Control-flow (conditionals)",
+        "Control-flow (loops)",
+        "Logic"
+      ]
+    },
     {
       "uuid": "cae4e000-3aac-41f7-b727-f9cce12d058d",
       "slug": "octal",

exercises/change/.meta/.version

@@ -0,0 +1 @@
+1

exercises/change/.meta/generator/change_case.rb

@@ -0,0 +1,9 @@
+require 'generator/exercise_case'
+
+class ChangeCase < Generator::ExerciseCase
+
+  def workload
+    assert_equal { "Change.generate(#{coins}, #{target})" }
+  end
+
+end

exercises/change/.meta/solutions/change.rb

@@ -0,0 +1,58 @@
+module BookKeeping
+  VERSION = 1
+end
+
+class Change
+  attr_reader :coins, :target
+
+  def initialize(coins, target)
+    @coins  = coins.sort.reverse
+    @target = target
+    @total_change = []
+  end
+
+  def generate
+    return [] if target.zero?
+
+    calculate_change(coins, [], target)
+
+    total_change.any? ? total_change.sort : -1
+  end
+
+  def self.generate(coins, target)
+    new(coins, target).generate
+  end
+
+  private
+
+  attr_accessor :total_change
+
+  def calculate_change(current_coins, current_change, current_value)
+    available_coins = current_coins.reject {|d| d > current_value } 
+
+    save_change(current_change) if current_value.zero?
+
+    return if has_more_coins?(current_change)
+
+    each_group(available_coins) do |coin, group|
+      calculate_change(group, current_change + [coin], current_value - coin)
+    end
+  end
+
+  def save_change(contents)
+    return if has_more_coins?(contents)
+
+    self.total_change = contents
+  end
+
+  def has_more_coins?(contents)
+    total_change.any? && (total_change.length < contents.length)
+  end
+
+  def each_group(array)
+    array.length.times do |n|
+      yield(array[n], array[n..-1])
+    end
+  end
+
+end

exercises/change/change_test.rb

@@ -0,0 +1,77 @@
+require 'minitest/autorun'
+require_relative 'change'
+
+# Common test data version: 1.0.0 3d8b5b3
+class ChangeTest < Minitest::Test
+  def test_single_coin_change
+    # skip
+    assert_equal [25], Change.generate([1, 5, 10, 25, 100], 25)
+  end
+
+  def test_multiple_coin_change
+    skip
+    assert_equal [5, 10], Change.generate([1, 5, 10, 25, 100], 15)
+  end
+
+  def test_change_with_lilliputian_coins
+    skip
+    assert_equal [4, 4, 15], Change.generate([1, 4, 15, 20, 50], 23)
+  end
+
+  def test_change_with_lower_elbonia_coins
+    skip
+    assert_equal [21, 21, 21], Change.generate([1, 5, 10, 21, 25], 63)
+  end
+
+  def test_large_target_values
+    skip
+    assert_equal [2, 2, 5, 20, 20, 50, 100, 100, 100, 100, 100, 100, 100, 100, 100], Change.generate([1, 2, 5, 10, 20, 50, 100], 999)
+  end
+
+  def test_possible_change_without_unit_coins_available
+    skip
+    assert_equal [2, 2, 2, 5, 10], Change.generate([2, 5, 10, 20, 50], 21)
+  end
+
+  def test_no_coins_make_0_change
+    skip
+    assert_equal [], Change.generate([1, 5, 10, 21, 25], 0)
+  end
+
+  def test_error_testing_for_change_smaller_than_the_smallest_of_coins
+    skip
+    assert_equal -1, Change.generate([5, 10], 3)
+  end
+
+  def test_error_if_no_combination_can_add_up_to_target
+    skip
+    assert_equal -1, Change.generate([5, 10], 94)
+  end
+
+  def test_cannot_find_negative_change_values
+    skip
+    assert_equal -1, Change.generate([1, 2, 5], -5)
+  end
+
+  # Problems in exercism evolve over time, as we find better ways to ask
+  # questions.
+  # The version number refers to the version of the problem you solved,
+  # not your solution.
+  #
+  # Define a constant named VERSION inside of the top level BookKeeping
+  # module, which may be placed near the end of your file.
+  #
+  # In your file, it will look like this:
+  #
+  # module BookKeeping
+  #   VERSION = 1 # Where the version number matches the one in the test.
+  # end
+  #
+  # If you are curious, read more about constants on RubyDoc:
+  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html
+
+  def test_bookkeeping
+    skip
+    assert_equal 1, BookKeeping::VERSION
+  end
+end