Recursive solution to cake thief

Author: robertwpaul

cake_thief/robertwpaul/cake_thief_recursion.rb

@@ -0,0 +1,20 @@
+Cake = Struct.new(:weight, :value)
+
+def pick_cakes(index, cakes, capacity)
+  return 0 if index == cakes.length || capacity.zero?
+
+  current_cake = cakes[index]
+
+  return pick_cakes(index + 1, cakes, capacity) if current_cake.weight > capacity
+
+  using_current = current_cake.value +
+                  pick_cakes(index, cakes, capacity - current_cake.weight)
+
+  not_using_current = pick_cakes(index + 1, cakes, capacity)
+
+  [using_current, not_using_current].max
+end
+
+def max_duffel_bag_value(cakes, capacity)
+  pick_cakes(0, cakes, capacity)
+end

cake_thief/robertwpaul/cake_thief_recursion_test.rb

@@ -0,0 +1,59 @@
+require 'minitest/autorun'
+require './cake_thief_recursion'
+
+class CakeThiefRecursionTest < Minitest::Test
+
+  def test_zero_capacity
+    cakes = [Cake.new(7, 160), Cake.new(3, 90), Cake.new(2, 15)]
+    capacity = 0
+    assert_equal 0, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_zero_cakes
+    cakes = []
+    capacity = 1000
+    assert_equal 0, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_one_cake_with_weight_equal_to_capacity
+    cakes = [Cake.new(5, 70)]
+    capacity = 5
+    assert_equal 70, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_cakes_with_spare_capacity
+    cakes = [Cake.new(3, 9), Cake.new(2, 4)]
+    capacity = 4
+    assert_equal 9, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_not_all_capacity_should_be_used
+    cakes = [Cake.new(5, 25), Cake.new(4, 16)]
+    capacity = 12
+    assert_equal 50, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_use_the_biggest_and_the_smallest
+    cakes = [Cake.new(3, 9), Cake.new(2, 4), Cake.new(1, 1)]
+    capacity = 4
+    assert_equal 10, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_use_a_really_valuable_small_cake
+    cakes = [Cake.new(3, 9), Cake.new(2, 4), Cake.new(1, 30)]
+    capacity = 4
+    assert_equal 120, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_arts_test
+    cakes = [Cake.new(3, 16), Cake.new(2, 15)]
+    capacity = 3
+    assert_equal 16, max_duffel_bag_value(cakes, capacity)
+  end
+
+  def test_interview_cake_test
+    cakes = [Cake.new(7, 160), Cake.new(3, 90), Cake.new(2, 15)]
+    capacity = 20
+    assert_equal 555, max_duffel_bag_value(cakes, capacity)
+  end
+end