Add knapsack exercise

config.json

@@ -889,6 +889,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 3
+      },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "254d5f19-d6fc-4c56-a8e2-f6d4e90ad4ec",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 1
       }
     ]
   },

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": [
+    "JohnMertz"
+  ],
+  "files": {
+    "solution": [
+      "lib/Knapsack.pm"
+    ],
+    "test": [
+      "t/knapsack.t"
+    ],
+    "example": [
+      ".meta/solutions/lib/Knapsack.pm"
+    ]
+  },
+  "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/solutions/lib/Knapsack.pm

@@ -0,0 +1,53 @@
+package Knapsack;
+
+use strict;
+use warnings;
+use experimental qw<signatures postderef postderef_qq>;
+
+use Exporter qw<import>;
+our @EXPORT_OK = qw<maximum_value>;
+
+sub maximum_value ( $items, $weight, $offset = 0, $best_score = 0, @indexes ) {
+
+    # Loop through all unchecked combinations of @indexes (the list of
+    # items passed from the last level of recursion), plus each of the
+    # items which appear later in the array (from the $offset index).
+    foreach my $index ( $offset .. $#$items ) {
+
+        # Reset local array of indexes from last loop iteration to that
+        # which was passed at the start of this level of recursion.
+        my @local_indexes = @indexes;
+
+        # Skip if this item exceeds remaining weight.
+        next if ( $items->[$index]->{'weight'} > $weight );
+
+        # Otherwise add item to knapsack
+        push( @local_indexes, $index );
+
+        # Calculate sum for new array of indexes
+        my $score = 0;
+        $score += $items->[$_]->{'value'} foreach @local_indexes;
+
+        # Overwrite $best_score if it has been beaten
+        $best_score = $score if ( $score > $best_score );
+
+        # Optimizations: Skip recursion if there is no capacity left
+        # or if there would be no additional items to check.
+        next if $weight == $items->[$index]->{'weight'};
+        next if ( $index == $#$items );
+
+        # Recursively call this function to check the remaining items
+        # in combination with the current @local_indexes. Offset the
+        # starting index to be the item after this one.
+        $best_score = maximum_value(
+            $items,
+            $weight - $items->[$index]->{'weight'},
+            ++$index,
+            $best_score,
+            @local_indexes
+        );
+    }
+    return $best_score;
+}
+
+1;

exercises/practice/knapsack/.meta/solutions/t/knapsack.t

@@ -0,0 +1 @@
+../../../t/knapsack.t

exercises/practice/knapsack/.meta/template-data.yaml

@@ -0,0 +1,60 @@
+subs: maximum_value
+
+properties:
+  maximumValue:
+    test: |-
+      use Data::Dmp;
+      sprintf(<<'END', dmp($case->{input}{items}), $case->{input}{maximumWeight}, $case->{expected}, dmp($case->{description}));
+      is(
+          maximum_value(%s, %s),
+          %s,
+          %s,
+      );
+      END
+
+stub: |-
+  sub maximum_value ($items, $weight) {
+      return undef;
+  }
+
+example: |-
+  sub maximum_value ($items, $weight, $offset=0, $best_score=0, @indexes) {
+
+      # Loop through all unchecked combinations of @indexes (the list of
+      # items passed from the last level of recursion), plus each of the
+      # items which appear later in the array (from the $offset index).
+      foreach my $index ($offset..$#$items) {
+          # Reset local array of indexes from last loop iteration to that
+          # which was passed at the start of this level of recursion.
+          my @local_indexes = @indexes;
+  
+          # Skip if this item exceeds remaining weight.
+          next if ($items->[$index]->{'weight'} > $weight);
+  
+          # Otherwise add item to knapsack
+          push (@local_indexes, $index);
+
+          # Calculate sum for new array of indexes
+          my $score = 0;
+          $score += $items->[$_]->{'value'} foreach @local_indexes;
+          # Overwrite $best_score if it has been beaten
+          $best_score = $score if ($score > $best_score);
+
+          # Optimizations: Skip recursion if there is no capacity left
+          # or if there would be no additional items to check.
+          next if $weight == $items->[$index]->{'weight'};
+          next if ($index == $#$items);
+  
+          # Recursively call this function to check the remaining items
+          # in combination with the current @local_indexes. Offset the
+          # starting index to be the item after this one.
+          $best_score = maximum_value(
+              $items,
+              $weight - $items->[$index]->{'weight'},
+              ++$index,
+              $best_score,
+              @local_indexes
+          );
+      }
+      return $best_score;
+  }

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/lib/Knapsack.pm

@@ -0,0 +1,12 @@
+package Knapsack;
+
+use v5.40;
+
+use Exporter qw<import>;
+our @EXPORT_OK = qw<maximum_value>;
+
+sub maximum_value ( $items, $weight ) {
+    return undef;
+}
+
+1;

exercises/practice/knapsack/t/knapsack.t

@@ -0,0 +1,51 @@
+#!/usr/bin/env perl
+use Test2::V0;
+
+use FindBin qw<$Bin>;
+use lib "$Bin/../lib", "$Bin/../local/lib/perl5";
+
+use Knapsack qw<maximum_value>;
+
+is( # begin: 3993a824-c20e-493d-b3c9-ee8a7753ee59
+    maximum_value( [], 100 ),
+    0,
+    "no items",
+); # end: 3993a824-c20e-493d-b3c9-ee8a7753ee59
+
+is( # begin: 1d39e98c-6249-4a8b-912f-87cb12e506b0
+    maximum_value( [ { value => 1, weight => 100 } ], 10 ),
+    0,
+    "one item, too heavy",
+); # end: 1d39e98c-6249-4a8b-912f-87cb12e506b0
+
+is( # begin: 833ea310-6323-44f2-9d27-a278740ffbd8
+    maximum_value( [ { value => 5, weight => 2 }, { value => 5, weight => 2 }, { value => 5, weight => 2 }, { value => 5, weight => 2 }, { value => 21, weight => 10 } ], 10 ),
+    21,
+    "five items (cannot be greedy by weight)",
+); # end: 833ea310-6323-44f2-9d27-a278740ffbd8
+
+is( # begin: 277cdc52-f835-4c7d-872b-bff17bab2456
+    maximum_value( [ { value => 20, weight => 2 }, { value => 20, weight => 2 }, { value => 20, weight => 2 }, { value => 20, weight => 2 }, { value => 50, weight => 10 } ], 10 ),
+    80,
+    "five items (cannot be greedy by value)",
+); # end: 277cdc52-f835-4c7d-872b-bff17bab2456
+
+is( # begin: 81d8e679-442b-4f7a-8a59-7278083916c9
+    maximum_value( [ { value => 10, weight => 5 }, { value => 40, weight => 4 }, { value => 30, weight => 6 }, { value => 50, weight => 4 } ], 10 ),
+    90,
+    "example knapsack",
+); # end: 81d8e679-442b-4f7a-8a59-7278083916c9
+
+is( # begin: f23a2449-d67c-4c26-bf3e-cde020f27ecc
+    maximum_value( [ { 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 } ], 104 ),
+    900,
+    "8 items",
+); # end: f23a2449-d67c-4c26-bf3e-cde020f27ecc
+
+is( # begin: 7c682ae9-c385-4241-a197-d2fa02c81a11
+    maximum_value( [ { 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 } ], 750 ),
+    1458,
+    "15 items",
+); # end: 7c682ae9-c385-4241-a197-d2fa02c81a11
+
+done_testing;