Add "Knapsack" exercise (#2757)

* generate files and create test generator

* init go modules

* move item struct to be in the exercise instead of generated test file

* create working example and fleshing out the Knapsack function

* Update config.json

* Prepare exercise for release

---------

Co-authored-by: André Santos <[email protected]>

config.json

@@ -1812,6 +1812,18 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "eae2fd23-c484-4dc6-b8fe-1fa055bab8ba",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6,
+        "topics": [
+          "algorithms",
+          "dynamic_programming"
+        ]
+      },
       {
         "slug": "dominoes",
         "name": "Dominoes",

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/config.json

@@ -0,0 +1,20 @@
+{
+  "authors": ["jesse-kroon"],
+  "files": {
+    "solution": [
+      "knapsack.go"
+    ],
+    "test": [
+      "knapsack_test.go"
+    ],
+    "editor": [
+      "cases_test.go"
+    ],
+    "example": [
+      ".meta/example.go"
+    ]
+  },
+  "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.go

@@ -0,0 +1,28 @@
+package knapsack
+
+import "math"
+
+type Item struct {
+	Weight, Value int
+}
+
+func Knapsack(maximumWeight int, items []Item) int {
+	amountOfItems := len(items)
+	knapsack := make([][]int, amountOfItems+1)
+
+	for i := range knapsack {
+		knapsack[i] = make([]int, maximumWeight+1)
+	}
+
+	for currentItem := 1; currentItem <= amountOfItems; currentItem++ {
+		for currentItemWeight := 0; currentItemWeight <= maximumWeight; currentItemWeight++ {
+			if items[currentItem-1].Weight > currentItemWeight {
+				knapsack[currentItem][currentItemWeight] = knapsack[currentItem-1][currentItemWeight]
+			} else {
+				knapsack[currentItem][currentItemWeight] = int(math.Max(float64(knapsack[currentItem-1][currentItemWeight]), float64(items[currentItem-1].Value+knapsack[currentItem-1][currentItemWeight-items[currentItem-1].Weight])))
+			}
+		}
+	}
+
+	return knapsack[amountOfItems][maximumWeight]
+}

exercises/practice/knapsack/.meta/gen.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"log"
+	"text/template"
+
+	"../../../../gen"
+)
+
+type item struct {
+	Weight int `json:"weight"`
+	Value  int `json:"value"`
+}
+type maximumValueCaseInput struct {
+	MaximumWeight int    `json:"maximumWeight"`
+	Items         []item `json:"items"`
+}
+
+type maximumValueCase struct {
+	Description string                `json:"description"`
+	Input       maximumValueCaseInput `json:"input"`
+	Expected    int                   `json:"expected"`
+}
+
+func main() {
+	t, err := template.New("").Parse(tmpl)
+	if err != nil {
+		log.Fatal(err)
+	}
+	var j = map[string]interface{}{
+		"maximumValue": &[]maximumValueCase{},
+	}
+	if err := gen.Gen("knapsack", j, t); err != nil {
+		log.Fatal(err)
+	}
+}
+
+var tmpl = `package knapsack
+
+{{.Header}}
+
+type maximumValueCaseInput struct {
+	MaximumWeight int
+	Items         []Item
+}
+
+type maximumValueTest struct {
+	description string       
+	input       maximumValueCaseInput
+	expected    int
+}	
+
+var maximumValueTests = []maximumValueTest { 
+	{{range .J.maximumValue}}
+		{
+			description: {{printf "%q" .Description}},
+			input: maximumValueCaseInput {
+				MaximumWeight: {{printf "%d" .Input.MaximumWeight}},
+				Items: []Item {
+					{{range .Input.Items}}
+						{
+							Weight: {{printf "%d" .Weight}},
+							Value: {{printf "%d" .Value}},
+						},
+					{{end}}
+				},
+			},
+			expected: {{printf "%d" .Expected}},
+		},
+	{{end}}
+}
+`

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"