Add knapsack exercise (#633)

config.json

@@ -1172,6 +1172,14 @@
         "prerequisites": [],
         "difficulty": 7
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "79cdfd22-2c85-46af-ac00-719ac89bd5a9",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "circular-buffer",
         "name": "Circular Buffer",

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 +1,19 @@
+{
+  "authors": [
+    "tomasnorre"
+  ],
+  "files": {
+    "solution": [
+      "Knapsack.php"
+    ],
+    "test": [
+      "KnapsackTest.php"
+    ],
+    "example": [
+      ".meta/example.php"
+    ]
+  },
+  "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.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+class Knapsack
+{
+    public function getMaximumValue(int $maximumWeight, array $items): int
+    {
+        $table = array_fill(0, count($items) + 1, array_fill(0, $maximumWeight + 1, 0));
+
+        for ($i = 0, $iMax = count($items); $i < $iMax; $i++) {
+            for ($capacity = 1; $capacity < $maximumWeight + 1; $capacity++) {
+                $value = $items[$i]['value'];
+                $weight = $items[$i]['weight'];
+                if ($weight > $capacity) {
+                    $table[$i + 1][$capacity] = $table[$i][$capacity];
+                } else {
+                    $table[$i + 1][$capacity] = max(
+                        $table[$i][$capacity],
+                        $value + $table[$i][$capacity - $weight]
+                    );
+                }
+            }
+        }
+
+        return $table[count($items)][$maximumWeight];
+    }
+}

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.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * By adding type hints and enabling strict type checking, code can become
+ * easier to read, self-documenting and reduce the number of potential bugs.
+ * By default, type declarations are non-strict, which means they will attempt
+ * to change the original type to match the type specified by the
+ * type-declaration.
+ *
+ * In other words, if you pass a string to a function requiring a float,
+ * it will attempt to convert the string value to a float.
+ *
+ * To enable strict mode, a single declare directive must be placed at the top
+ * of the file.
+ * This means that the strictness of typing is configured on a per-file basis.
+ * This directive not only affects the type declarations of parameters, but also
+ * a function's return type.
+ *
+ * For more info review the Concept on strict type checking in the PHP track
+ * <link>.
+ *
+ * To disable strict typing, comment out the directive below.
+ */
+
+declare(strict_types=1);
+
+class Knapsack
+{
+    public function getMaximumValue(int $maximumWeight, array $items): int
+    {
+        throw new \BadMethodCallException(sprintf('Implement the %s method', __FUNCTION__));
+    }
+}

exercises/practice/knapsack/KnapsackTest.php

@@ -0,0 +1,124 @@
+<?php
+
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+
+class KnapsackTest extends TestCase
+{
+    private Knapsack $knapsack;
+
+    public static function setUpBeforeClass(): void
+    {
+        require_once 'Knapsack.php';
+    }
+
+    protected function setUp(): void
+    {
+        $this->knapsack = new Knapsack();
+    }
+
+    /**
+     * uuid: 3993a824-c20e-493d-b3c9-ee8a7753ee59
+     */
+    public function testNoItems(): void
+    {
+        $this->assertEquals(0, $this->knapsack->getMaximumValue(100, []));
+    }
+
+    /**
+     * uuid: 1d39e98c-6249-4a8b-912f-87cb12e506b0
+     */
+    public function testOneItemTooHeavy(): void
+    {
+        $items = [[ 'weight' => 100, 'value' => 1 ]];
+        $this->assertEquals(0, $this->knapsack->getMaximumValue(10, $items));
+    }
+
+    /**
+     * uuid: 833ea310-6323-44f2-9d27-a278740ffbd8
+     */
+    public function testFiveItemsCannotBeGreedyByWeight(): void
+    {
+        $items = [
+            [ 'weight' => 2, 'value' => 5 ],
+            [ 'weight' => 2, 'value' => 5 ],
+            [ 'weight' => 2, 'value' => 5 ],
+            [ 'weight' => 2, 'value' => 5 ],
+            [ 'weight' => 10, 'value' => 21 ],
+        ];
+        $this->assertEquals(21, $this->knapsack->getMaximumValue(10, $items));
+    }
+
+    /**
+     * uuid: 277cdc52-f835-4c7d-872b-bff17bab2456
+     */
+    public function testFiveItemsCannotBeGreedyByValue(): void
+    {
+        $items = [
+            [ 'weight' => 2, 'value' => 20 ],
+            [ 'weight' => 2, 'value' => 20 ],
+            [ 'weight' => 2, 'value' => 20 ],
+            [ 'weight' => 2, 'value' => 20 ],
+            [ 'weight' => 10, 'value' => 50 ],
+        ];
+        $this->assertEquals(80, $this->knapsack->getMaximumValue(10, $items));
+    }
+
+    /**
+     * uuid: 81d8e679-442b-4f7a-8a59-7278083916c9
+     */
+    public function testExampleKnapsack(): void
+    {
+        $items = [
+            [ 'weight' => 5, 'value' => 10 ],
+            [ 'weight' => 4, 'value' => 40 ],
+            [ 'weight' => 6, 'value' => 30 ],
+            [ 'weight' => 4, 'value' => 50 ],
+        ];
+        $this->assertEquals(90, $this->knapsack->getMaximumValue(10, $items));
+    }
+
+    /**
+     * uuid: f23a2449-d67c-4c26-bf3e-cde020f27ecc
+     */
+    public function testEightItems(): void
+    {
+        $items = [
+            [ 'weight' => 25, 'value' => 350 ],
+            [ 'weight' => 35, 'value' => 400 ],
+            [ 'weight' => 45, 'value' => 450 ],
+            [ 'weight' => 5, 'value' => 20 ],
+            [ 'weight' => 25, 'value' => 70 ],
+            [ 'weight' => 3, 'value' => 8 ],
+            [ 'weight' => 2, 'value' => 5 ],
+            [ 'weight' => 2, 'value' => 5 ],
+        ];
+        $this->assertEquals(900, $this->knapsack->getMaximumValue(104, $items));
+    }
+
+    /**
+     * uuid: 7c682ae9-c385-4241-a197-d2fa02c81a11
+     */
+    public function testFifteenItems(): void
+    {
+        $items = [
+            [ 'weight' => 70, 'value' => 135 ],
+            [ 'weight' => 73, 'value' => 139 ],
+            [ 'weight' => 77, 'value' => 149 ],
+            [ 'weight' => 80, 'value' => 150 ],
+            [ 'weight' => 82, 'value' => 156 ],
+            [ 'weight' => 87, 'value' => 163 ],
+            [ 'weight' => 90, 'value' => 173 ],
+            [ 'weight' => 94, 'value' => 184 ],
+            [ 'weight' => 98, 'value' => 192 ],
+            [ 'weight' => 106, 'value' => 201 ],
+            [ 'weight' => 110, 'value' => 210 ],
+            [ 'weight' => 113, 'value' => 214 ],
+            [ 'weight' => 115, 'value' => 221 ],
+            [ 'weight' => 118, 'value' => 229 ],
+            [ 'weight' => 120, 'value' => 240 ],
+        ];
+        $this->assertEquals(1458, $this->knapsack->getMaximumValue(750, $items));
+    }
+}