Add Knapsack exercise (#1661)

* Add knapsack exercise

* Underscore unused params, turn string diff to int diff

Author: dem4ron

config.json

@@ -1508,6 +1508,14 @@
         ],
         "status": "deprecated"
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "cbccd0c5-eb15-4705-9a4c-0209861f078c",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "kindergarten-garden",
         "name": "Kindergarten Garden",

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

@@ -0,0 +1,32 @@
+# 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 pairs, `wi` and `vi`, where the first element `wi` is the weight of the *i*th item and `vi` is the value for that item.
+
+For example:
+
+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/.gitignore

@@ -0,0 +1,8 @@
+# Generated by Cargo
+# Will have compiled files and executables
+/target/
+**/*.rs.bk
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
+Cargo.lock

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

@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "dem4ron"
+  ],
+  "files": {
+    "solution": [
+      "src/lib.rs",
+      "Cargo.toml"
+    ],
+    "test": [
+      "tests/knapsack.rs"
+    ],
+    "example": [
+      ".meta/example.rs"
+    ]
+  },
+  "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.rs

@@ -0,0 +1,26 @@
+pub struct Item {
+    pub weight: u32,
+    pub value: u32,
+}
+
+pub fn maximum_value(max_weight: u32, items: Vec<Item>) -> u32 {
+    let mut max_values = vec![vec![0; (max_weight + 1) as usize]; items.len() + 1];
+
+    for i in 1..=items.len() {
+        let item_weight = items[i - 1].weight as usize;
+        let item_value = items[i - 1].value;
+
+        for w in 0..=(max_weight as usize) {
+            if item_weight <= w {
+                max_values[i][w] = std::cmp::max(
+                    max_values[i - 1][w],
+                    max_values[i - 1][w - item_weight] + item_value,
+                );
+            } else {
+                max_values[i][w] = max_values[i - 1][w];
+            }
+        }
+    }
+
+    max_values[items.len()][max_weight as usize]
+}

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

@@ -0,0 +1,31 @@
+# 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"
+
+[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/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "knapsack"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

exercises/practice/knapsack/src/lib.rs

@@ -0,0 +1,8 @@
+pub struct Item {
+    pub weight: u32,
+    pub value: u32,
+}
+
+pub fn maximum_value(_max_weight: u32, _items: Vec<Item>) -> u32 {
+    unimplemented!("Solve the knapsack exercise");
+}

exercises/practice/knapsack/tests/knapsack.rs

@@ -0,0 +1,219 @@
+use knapsack::*;
+
+#[test]
+fn test_example_knapsack() {
+    let max_weight = 10;
+    let items = vec![
+        Item {
+            weight: 5,
+            value: 10,
+        },
+        Item {
+            weight: 4,
+            value: 40,
+        },
+        Item {
+            weight: 6,
+            value: 30,
+        },
+        Item {
+            weight: 4,
+            value: 50,
+        },
+    ];
+
+    assert_eq!(maximum_value(max_weight, items), 90);
+}
+
+#[test]
+#[ignore]
+fn test_no_items() {
+    let max_weight = 100;
+    let items = vec![];
+
+    assert_eq!(maximum_value(max_weight, items), 0);
+}
+
+#[test]
+#[ignore]
+fn test_one_item_too_heavy() {
+    let max_weight = 10;
+    let items = vec![Item {
+        weight: 100,
+        value: 1,
+    }];
+
+    assert_eq!(maximum_value(max_weight, items), 0);
+}
+
+#[test]
+#[ignore]
+fn test_five_items_cannot_be_greedy_by_weight() {
+    let max_weight = 10;
+    let items = vec![
+        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,
+        },
+    ];
+
+    assert_eq!(maximum_value(max_weight, items), 21);
+}
+
+#[test]
+#[ignore]
+fn test_five_items_cannot_be_greedy_by_value() {
+    let max_weight = 10;
+    let items = vec![
+        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,
+        },
+    ];
+
+    assert_eq!(maximum_value(max_weight, items), 80);
+}
+
+#[test]
+#[ignore]
+fn test_8_items() {
+    let max_weight = 104;
+    let items = vec![
+        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,
+        },
+    ];
+
+    assert_eq!(maximum_value(max_weight, items), 900);
+}
+
+#[test]
+#[ignore]
+fn test_15_items() {
+    let max_weight = 750;
+    let items = vec![
+        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,
+        },
+    ];
+
+    assert_eq!(maximum_value(max_weight, items), 1458);
+}