Added Knapcask exercise (#1199)

Add Knapcask exercise

---------

Co-authored-by: Erik Schierboom <erik_schierboom@hotmail.com>

config.json

@@ -489,6 +489,17 @@
           "maybe"
         ]
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "1be3e783-d240-4a4b-bb45-ff2ce4d36374",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7,
+        "topics": [
+          "algorithms"
+        ]
+      },
       {
         "slug": "go-counting",
         "name": "Go Counting",

exercises/practice/knapsack/.docs/instructions.md

@@ -0,0 +1,35 @@
+# Instructions
+
+In this exercise, let's try to solve a classic problem.
+
+Bob is a thief.
+After months of careful planning, he finally manages to crack the security systems of a high-class apartment.
+
+In front of him are many items, each with a value (v) and weight (w).
+Bob, of course, wants to maximize the total value he can get; he would gladly take all of the items if he could.
+However, to his horror, he realizes that the knapsack he carries with him can only hold so much weight (W).
+
+Given a knapsack with a specific carrying capacity (W), help Bob determine the maximum value he can get from the items in the house.
+Note that Bob can take only one of each item.
+
+All values given will be strictly positive.
+Items will be represented as a list of items.
+Each item will have a weight and value.
+
+For example:
+
+```none
+Items: [
+  { "weight": 5, "value": 10 },
+  { "weight": 4, "value": 40 },
+  { "weight": 6, "value": 30 },
+  { "weight": 4, "value": 50 }
+]
+
+Knapsack Limit: 10
+```
+
+For the above, the first item has weight 5 and value 10, the second item has weight 4 and value 40, and so on.
+
+In this example, Bob should take the second and fourth item to maximize his value, which, in this case, is 90.
+He cannot get more than 90 as his knapsack has a weight limit of 10.

exercises/practice/knapsack/.meta/config.json

@@ -0,0 +1,23 @@
+{
+  "authors": [
+    "tofische"
+  ],
+  "files": {
+    "solution": [
+      "src/Knapsack.hs",
+      "package.yaml"
+    ],
+    "test": [
+      "test/Tests.hs"
+    ],
+    "example": [
+      ".meta/examples/success-standard/src/Knapsack.hs"
+    ],
+    "invalidator": [
+      "stack.yaml"
+    ]
+  },
+  "blurb": "Given a knapsack that can only carry a certain weight, determine which items to put in the knapsack in order to maximize their combined value.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Knapsack_problem"
+}

exercises/practice/knapsack/.meta/examples/success-standard/package.yaml

@@ -0,0 +1,16 @@
+name: knapsack
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: Knapsack
+  source-dirs: src
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - knapsack
+      - hspec

exercises/practice/knapsack/.meta/examples/success-standard/src/Knapsack.hs

@@ -0,0 +1,15 @@
+module Knapsack (maximumValue) where
+
+type Item = (Int, Int)
+type Items = [Item]
+
+maximumValue :: Int -> Items -> Int
+maximumValue n items = maximum $ fst <$> solve n items
+
+solve :: Int -> Items -> [(Int, Items)]
+solve _ [] = [(0, [])]
+solve limit (item@(w,v):rest) = if w > limit then withoutItem else withoutItem <> withItem
+    where
+        withoutItem = solve limit rest
+        withItem = prependItem <$> solve (limit-w) rest
+        prependItem (val, lst) = (val + v, item:lst)

exercises/practice/knapsack/.meta/tests.toml

@@ -0,0 +1,36 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[a4d7d2f0-ad8a-460c-86f3-88ba709d41a7]
+description = "no items"
+include = false
+
+[3993a824-c20e-493d-b3c9-ee8a7753ee59]
+description = "no items"
+reimplements = "a4d7d2f0-ad8a-460c-86f3-88ba709d41a7"
+
+[1d39e98c-6249-4a8b-912f-87cb12e506b0]
+description = "one item, too heavy"
+
+[833ea310-6323-44f2-9d27-a278740ffbd8]
+description = "five items (cannot be greedy by weight)"
+
+[277cdc52-f835-4c7d-872b-bff17bab2456]
+description = "five items (cannot be greedy by value)"
+
+[81d8e679-442b-4f7a-8a59-7278083916c9]
+description = "example knapsack"
+
+[f23a2449-d67c-4c26-bf3e-cde020f27ecc]
+description = "8 items"
+
+[7c682ae9-c385-4241-a197-d2fa02c81a11]
+description = "15 items"

exercises/practice/knapsack/package.yaml

@@ -0,0 +1,21 @@
+name: knapsack
+version: 1.0.0.0
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: Knapsack
+  source-dirs: src
+  ghc-options: -Wall
+  # dependencies:
+  # - foo       # List here the packages you
+  # - bar       # want to use in your solution.
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - knapsack
+      - hspec

exercises/practice/knapsack/src/Knapsack.hs

@@ -0,0 +1,4 @@
+module Knapsack (maximumValue) where
+
+maximumValue :: Int -> [(Int, Int)] -> Int
+maximumValue n items = error "You need to implement this function."

exercises/practice/knapsack/stack.yaml

@@ -0,0 +1 @@
+resolver: lts-20.18

exercises/practice/knapsack/test/Tests.hs

@@ -0,0 +1,84 @@
+{-# LANGUAGE RecordWildCards #-}
+
+import Data.Foldable     (for_)
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFailFast, defaultConfig, hspecWith)
+
+import Knapsack (maximumValue)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFailFast = True} specs
+
+specs :: Spec
+specs = describe "valid" $ for_ cases test
+  where
+    test Case{..} = it description $ maximumValue input1 input2 `shouldBe` expected
+
+data Case = Case { description :: String
+                 , input1      :: Int
+                 , input2      :: [(Int, Int)]
+                 , expected    :: Int
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "no items"
+               , input1      = 100
+               , input2      = []
+               , expected    = 0
+               }
+        , Case { description = "one item, too heavy"
+               , input1      = 10
+               , input2      = [(100, 1)]
+               , expected    = 0
+               }
+        , Case { description = "five items (cannot be greedy by weight)"
+               , input1      = 10
+               , input2      = [(2, 5), (2, 5), (2, 5), (2, 5), (10, 21)]
+               , expected    = 21
+               }
+        , Case { description = "five items (cannot be greedy by value)"
+               , input1      = 10
+               , input2      = [(2, 20), (2, 20), (2, 20), (2, 20), (10, 50)]
+               , expected    = 80
+               }
+        , Case { description = "example knapsack"
+               , input1      = 10
+               , input2      = [(5, 10), (4, 40), (6, 30), (4, 50)]
+               , expected    = 90
+               }
+        , Case { description = "8 items"
+               , input1      = 104
+               , input2      = [
+                                   (25, 350),
+                                   (35, 400),
+                                   (45, 450),
+                                   (5, 20),
+                                   (25, 70),
+                                   (3, 8),
+                                   (2, 5),
+                                   (2, 5)
+                                ]
+               , expected    = 900
+               }
+        , Case { description = "15 items"
+               , input1      = 750
+               , input2      = [
+                                   (70, 135),
+                                   (73, 139),
+                                   (77, 149),
+                                   (80, 150),
+                                   (82, 156),
+                                   (87, 163),
+                                   (90, 173),
+                                   (94, 184),
+                                   (98, 192),
+                                   (106, 201),
+                                   (110, 210),
+                                   (113, 214),
+                                   (115, 221),
+                                   (118, 229),
+                                   (120, 240)
+                               ]
+               , expected    = 1458
+               }
+        ]