Add knapsack

config.json

@@ -722,6 +722,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "67cca2b4-9e4e-43f6-9e17-a3d7d291015f",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "matching-brackets",
         "name": "Matching Brackets",

exercises/practice/knapsack/.busted

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

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

@@ -0,0 +1,25 @@
+# Instructions
+
+Your task is to determine which items to take so that the total value of her selection is maximized, taking into account the knapsack's carrying capacity.
+
+Items will be represented as a list of items.
+Each item will have a weight and value.
+All values given will be strictly positive.
+Lhakpa can take only one of each item.
+
+For example:
+
+```text
+Items: [
+  { "weight": 5, "value": 10 },
+  { "weight": 4, "value": 40 },
+  { "weight": 6, "value": 30 },
+  { "weight": 4, "value": 50 }
+]
+
+Knapsack Maximum Weight: 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, Lhakpa should take the second and fourth item to maximize her value, which, in this case, is 90.
+She cannot get more than 90 as her knapsack has a weight limit of 10.

exercises/practice/knapsack/.docs/introduction.md

@@ -0,0 +1,10 @@
+# Introduction
+
+Lhakpa is a [Sherpa][sherpa] mountain guide and porter.
+After months of careful planning, the expedition Lhakpa works for is about to leave.
+She will be paid the value she carried to the base camp.
+
+In front of her are many items, each with a value and weight.
+Lhakpa would gladly take all of the items, but her knapsack can only hold so much weight.
+
+[sherpa]: https://en.wikipedia.org/wiki/Sherpa_people#Mountaineering

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "knapsack.moon"
+    ],
+    "test": [
+      "knapsack_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "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/example.moon

@@ -0,0 +1,16 @@
+-- following pseudocode under
+-- https://en.wikipedia.org/wiki/Knapsack_problem#0-1_knapsack_problem
+{ 
+  maximumValue: (maxWt, items) ->
+    n = #items
+    -- using table comprehension syntax
+    -- because we need to have index 0 in both dimensions
+    m = {i, {j, 0 for j = 0, maxWt} for i = 0, n}
+    for i = 1, n
+      for j = 1, maxWt
+        if items[i].weight > j
+          m[i][j] = m[i - 1][j]
+        else
+          m[i][j] = math.max(m[i - 1][j], m[i - 1][j - items[i].weight] + items[i].value)
+    m[n][maxWt] 
+}

exercises/practice/knapsack/.meta/spec_generator.moon

@@ -0,0 +1,14 @@
+import table_list from require 'test_helpers'
+
+{
+  module_imports: {'maximumValue'},
+
+  generate_test: (case, level) ->
+    lines = {
+      "items = #{table_list case.input.items, level}",
+      "maxWeight = #{case.input.maximumWeight}",
+      "result = maximumValue maxWeight, items",
+      "assert.are.equal #{case.expected}, result"
+    }
+    table.concat [indent line, level for line in *lines], '\n'
+}

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/knapsack_spec.moon

@@ -0,0 +1,86 @@
+import maximumValue from require 'knapsack'
+
+describe 'knapsack', ->
+  it 'no items', ->
+    items = {}
+    maxWeight = 100
+    result = maximumValue maxWeight, items
+    assert.are.equal 0, result
+
+  pending 'one item, too heavy', ->
+    items = {{value: 1, weight: 100}}
+    maxWeight = 10
+    result = maximumValue maxWeight, items
+    assert.are.equal 0, result
+
+  pending 'five items (cannot be greedy by weight)', ->
+    items = {
+      {value: 5, weight: 2},
+      {value: 5, weight: 2},
+      {value: 5, weight: 2},
+      {value: 5, weight: 2},
+      {value: 21, weight: 10},
+    }
+    maxWeight = 10
+    result = maximumValue maxWeight, items
+    assert.are.equal 21, result
+
+  pending 'five items (cannot be greedy by value)', ->
+    items = {
+      {value: 20, weight: 2},
+      {value: 20, weight: 2},
+      {value: 20, weight: 2},
+      {value: 20, weight: 2},
+      {value: 50, weight: 10},
+    }
+    maxWeight = 10
+    result = maximumValue maxWeight, items
+    assert.are.equal 80, result
+
+  pending 'example knapsack', ->
+    items = {
+      {value: 10, weight: 5},
+      {value: 40, weight: 4},
+      {value: 30, weight: 6},
+      {value: 50, weight: 4},
+    }
+    maxWeight = 10
+    result = maximumValue maxWeight, items
+    assert.are.equal 90, result
+
+  pending '8 items', ->
+    items = {
+      {value: 350, weight: 25},
+      {value: 400, weight: 35},
+      {value: 450, weight: 45},
+      {value: 20, weight: 5},
+      {value: 70, weight: 25},
+      {value: 8, weight: 3},
+      {value: 5, weight: 2},
+      {value: 5, weight: 2},
+    }
+    maxWeight = 104
+    result = maximumValue maxWeight, items
+    assert.are.equal 900, result
+
+  pending '15 items', ->
+    items = {
+      {value: 135, weight: 70},
+      {value: 139, weight: 73},
+      {value: 149, weight: 77},
+      {value: 150, weight: 80},
+      {value: 156, weight: 82},
+      {value: 163, weight: 87},
+      {value: 173, weight: 90},
+      {value: 184, weight: 94},
+      {value: 192, weight: 98},
+      {value: 201, weight: 106},
+      {value: 210, weight: 110},
+      {value: 214, weight: 113},
+      {value: 221, weight: 115},
+      {value: 229, weight: 118},
+      {value: 240, weight: 120},
+    }
+    maxWeight = 750
+    result = maximumValue maxWeight, items
+    assert.are.equal 1458, result

lib/test_helpers.moon

@@ -95,6 +95,17 @@ table_tostring_ordered = (t, keys) ->
   s = [string.format '%s: %q', k, t[k] for k in *keys]
   "{#{table.concat s, ', '}}"
 
+--- list of one-line key-value tables
+table_list = (list, level) ->
+  error 'Provide a level for `table_list`', 2 if not level
+  if #list <= 1
+    "{#{table.concat [table_tostring elem for elem in *list], ', '}}"
+  else
+    lines = [indent table_tostring(elem) .. ',', level + 1 for elem in *list]
+    table.insert lines, 1, '{'
+    table.insert lines, indent('}', level)
+    table.concat lines, '\n'
+
 --- Table contains an element
 table_contains = (list, target) ->
   for elem in *list
@@ -154,6 +165,7 @@ table_dump = (what, level = 0) ->
   :kv_table
   :table_tostring
   :table_tostring_ordered
+  :table_list
   :json_string
   :table_contains
   :table_dump