Add Knapsack exercise (#768)

* Add Knapsack exercise

* Revert formatting change to track config.json

* Undo accidental indent_size change

* Change indenting to 2 spaces

This is to be consistent with the other exercises that already use 2
spaces.

config.json

@@ -838,6 +838,14 @@
         "difficulty": 5,
         "topics": ["algorithms", "text_formatting"]
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "1e5a75f5-b269-4297-a6db-d148d81eee5a",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "linked-list",
         "name": "Linked List",

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

@@ -0,0 +1,3 @@
+## Item representation
+
+The items are represented by the `Item` struct in `Item.swift`.

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 his 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.
+Bob 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, 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/.docs/introduction.md

@@ -0,0 +1,8 @@
+# Introduction
+
+Bob is a thief.
+After months of careful planning, he finally manages to crack the security systems of a fancy store.
+
+In front of him are many items, each with a value and weight.
+Bob would gladly take all of the items, but his knapsack can only hold so much weight.
+Bob has to carefully consider which items to take so that the total value of his selection is maximized.

exercises/practice/knapsack/.meta/Sources/Knapsack/Item.swift

@@ -0,0 +1,7 @@
+// Represents an item in knapsack.
+// There is be no need to edit this file and changes to this file are ignored by the Exercism test runners.
+
+struct Item {
+  let weight: Int
+  let value: Int
+}

exercises/practice/knapsack/.meta/Sources/Knapsack/KnapsackExample.swift

@@ -0,0 +1,22 @@
+struct Knapsack {
+  static func maximumValue(_ items: [Item], _ capacity: Int) -> Int {
+    if items.count == 0 {
+      return 0
+    }
+
+    var values: Array<Int> = Array(repeating: 0, count: capacity + 1)
+    for item in items {
+      var next: Array<Int> = Array(repeating: 0, count: values.count)
+      for i in 0..<values.count {
+        if item.weight <= i {
+          let valueWith = values[i - item.weight] + item.value
+          next[i] = max(valueWith, values[i])
+        } else {
+          next[i] = values[i]
+        }
+      }
+      values = next
+    }
+    return values.last!
+  }
+}

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

@@ -0,0 +1,22 @@
+{
+  "authors": [
+    "kahgoh"
+  ],
+  "files": {
+    "solution": [
+      "Sources/Knapsack/Knapsack.swift"
+    ],
+    "test": [
+      "Tests/KnapsackTests/KnapsackTests.swift"
+    ],
+    "example": [
+      ".meta/Sources/Knapsack/KnapsackExample.swift"
+    ],
+    "editor": [
+      "Sources/Knapsack/Item.swift"
+    ]
+  },
+  "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/template.swift

@@ -0,0 +1,22 @@
+import XCTest
+@testable import {{exercise|camelCase}}
+class {{exercise|camelCase}}Tests: XCTestCase {
+    let runAll = Bool(ProcessInfo.processInfo.environment["RUNALL", default: "false"]) ?? false
+
+    {% for case in cases %}
+    {%- if forloop.first %}
+        func test{{case.description |camelCase}}() {
+    {%- else %}
+        func test{{case.description |camelCase}}() throws {
+            try XCTSkipIf(true && !runAll) // change true to false to run this test
+    {%- endif %}
+
+            let items : [Item] = [
+            {%- for item in case.input.items %}
+                {{item | knapsackItem}},
+            {%- endfor -%}
+            ]
+            XCTAssertEqual(Knapsack.maximumValue(items, {{case.input.maximumWeight}}), {{case.expected}})
+        }
+    {% endfor -%}
+}

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.swift

@@ -0,0 +1,21 @@
+// swift-tools-version:5.3
+
+import PackageDescription
+
+let package = Package(
+  name: "Knapsack",
+  products: [
+    .library(
+      name: "Knapsack",
+      targets: ["Knapsack"])
+  ],
+  dependencies: [],
+  targets: [
+    .target(
+      name: "Knapsack",
+      dependencies: []),
+    .testTarget(
+      name: "KnapsackTests",
+      dependencies: ["Knapsack"]),
+  ]
+)

exercises/practice/knapsack/Sources/Knapsack/Item.swift

@@ -0,0 +1,7 @@
+// Represents an item in knapsack.
+// There is be no need to edit this file and changes to this file are ignored by the Exercism test runners.
+
+struct Item {
+  let weight: Int
+  let value: Int
+}

exercises/practice/knapsack/Sources/Knapsack/Knapsack.swift

@@ -0,0 +1,3 @@
+struct Knapsack {
+  // Write your code for the 'Knapsack' exercise in this file.
+}

exercises/practice/knapsack/Tests/KnapsackTests/KnapsackTests.swift

@@ -0,0 +1,99 @@
+import XCTest
+
+@testable import Knapsack
+
+class KnapsackTests: XCTestCase {
+  let runAll = Bool(ProcessInfo.processInfo.environment["RUNALL", default: "false"]) ?? false
+
+  func testNoItems() {
+
+    let items: [Item] = []
+    XCTAssertEqual(Knapsack.maximumValue(items, 100), 0)
+  }
+
+  func testOneItemTooHeavy() throws {
+    try XCTSkipIf(true && !runAll)  // change true to false to run this test
+
+    let items: [Item] = [
+      Item(weight: 100, value: 1)
+    ]
+    XCTAssertEqual(Knapsack.maximumValue(items, 10), 0)
+  }
+
+  func testFiveItemsCannotBeGreedyByWeight() throws {
+    try XCTSkipIf(true && !runAll)  // change true to false to run this test
+
+    let items: [Item] = [
+      Item(weight: 2, value: 5),
+      Item(weight: 2, value: 5),
+      Item(weight: 2, value: 5),
+      Item(weight: 2, value: 5),
+      Item(weight: 10, value: 21),
+    ]
+    XCTAssertEqual(Knapsack.maximumValue(items, 10), 21)
+  }
+
+  func testFiveItemsCannotBeGreedyByValue() throws {
+    try XCTSkipIf(true && !runAll)  // change true to false to run this test
+
+    let items: [Item] = [
+      Item(weight: 2, value: 20),
+      Item(weight: 2, value: 20),
+      Item(weight: 2, value: 20),
+      Item(weight: 2, value: 20),
+      Item(weight: 10, value: 50),
+    ]
+    XCTAssertEqual(Knapsack.maximumValue(items, 10), 80)
+  }
+
+  func testExampleKnapsack() throws {
+    try XCTSkipIf(true && !runAll)  // change true to false to run this test
+
+    let items: [Item] = [
+      Item(weight: 5, value: 10),
+      Item(weight: 4, value: 40),
+      Item(weight: 6, value: 30),
+      Item(weight: 4, value: 50),
+    ]
+    XCTAssertEqual(Knapsack.maximumValue(items, 10), 90)
+  }
+
+  func test8Items() throws {
+    try XCTSkipIf(true && !runAll)  // change true to false to run this test
+
+    let items: [Item] = [
+      Item(weight: 25, value: 350),
+      Item(weight: 35, value: 400),
+      Item(weight: 45, value: 450),
+      Item(weight: 5, value: 20),
+      Item(weight: 25, value: 70),
+      Item(weight: 3, value: 8),
+      Item(weight: 2, value: 5),
+      Item(weight: 2, value: 5),
+    ]
+    XCTAssertEqual(Knapsack.maximumValue(items, 104), 900)
+  }
+
+  func test15Items() throws {
+    try XCTSkipIf(true && !runAll)  // change true to false to run this test
+
+    let items: [Item] = [
+      Item(weight: 70, value: 135),
+      Item(weight: 73, value: 139),
+      Item(weight: 77, value: 149),
+      Item(weight: 80, value: 150),
+      Item(weight: 82, value: 156),
+      Item(weight: 87, value: 163),
+      Item(weight: 90, value: 173),
+      Item(weight: 94, value: 184),
+      Item(weight: 98, value: 192),
+      Item(weight: 106, value: 201),
+      Item(weight: 110, value: 210),
+      Item(weight: 113, value: 214),
+      Item(weight: 115, value: 221),
+      Item(weight: 118, value: 229),
+      Item(weight: 120, value: 240),
+    ]
+    XCTAssertEqual(Knapsack.maximumValue(items, 750), 1458)
+  }
+}

generator/Sources/Generator/generator-plugins.swift

@@ -232,6 +232,15 @@ class GeneratorPlugins {
       return nil
     }
 
+    ext.registerFilter("knapsackItem") { (value: Any?) in
+      if let item = value as? [String: Any] {
+        let itemWeight = String(describing: item["weight", default: ""])
+        let itemValue = String(describing: item["value", default: ""])
+        return "Item(weight:\(itemWeight), value:\(itemValue))"
+      }
+      return "// Something else ..."
+    }
+
     let environment = Environment(extensions: [ext])
     return environment
   }