Add collatz-conjecture exercise

config.json

@@ -235,6 +235,14 @@
         "prerequisites": [],
         "difficulty": 1
       },
+      {
+        "slug": "collatz-conjecture",
+        "name": "Collatz Conjecture",
+        "uuid": "d952ed69-1598-449b-a28e-7dfd19b53f89",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "crypto-square",
         "name": "Crypto Square",

exercises/practice/collatz-conjecture/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+Take any positive integer n.
+If n is even, divide n by 2 to get n / 2.
+If n is odd, multiply n by 3 and add 1 to get 3n + 1.
+Repeat the process indefinitely.
+The conjecture states that no matter which number you start with, you will always reach 1 eventually.
+
+Given a number n, return the number of steps required to reach 1.
+
+## Examples
+
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps.
+So for input n = 12, the return value would be 9.

exercises/practice/collatz-conjecture/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "lib/CollatzConjecture.pm"
+    ],
+    "test": [
+      "t/collatz-conjecture.t"
+    ],
+    "example": [
+      ".meta/solutions/lib/CollatzConjecture.pm"
+    ]
+  },
+  "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
+  "source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
+  "source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
+}

exercises/practice/collatz-conjecture/.meta/solutions/lib/CollatzConjecture.pm

@@ -0,0 +1,20 @@
+package CollatzConjecture;
+
+use strict;
+use warnings;
+use experimental qw<signatures postderef postderef_qq>;
+
+use Exporter qw<import>;
+our @EXPORT_OK = qw<steps>;
+
+sub steps ($number) {
+    die 'Only positive integers are allowed' unless $number > 0;
+    my $count = 0;
+    while ( $number > 1 ) {
+        $number = ( $number % 2 == 0 ) ? ( $number / 2 ) : ( 3 * $number + 1 );
+        $count++;
+    }
+    return $count;
+}
+
+1;

exercises/practice/collatz-conjecture/.meta/solutions/t/collatz-conjecture.t

@@ -0,0 +1 @@
+../../../t/collatz-conjecture.t

exercises/practice/collatz-conjecture/.meta/template-data.yaml

@@ -0,0 +1,39 @@
+subs: steps
+properties:
+  steps:
+    test: |-
+      use Data::Dmp;
+      if (ref $case->{expected}) {
+          sprintf(<<'END', $case->{input}{number}, $case->{expected}{error}, dmp($case->{description}));
+      like(
+          dies( sub { steps(%s) } ),
+          qr/%s/,
+          %s,
+      );
+      END
+      }
+      else {
+          sprintf(<<'END', $case->{input}{number}, $case->{expected}, dmp($case->{description}));
+      is(
+          steps(%s),
+          %s,
+          %s,
+      );
+      END
+      }
+
+stub: |-
+  sub steps ($number) {
+    return undef;
+  }
+
+example: |-
+  sub steps ($number) {
+    die 'Only positive integers are allowed' unless $number > 0;
+    my $count = 0;
+    while ($number > 1) {
+      $number = ($number % 2 == 0) ? ($number / 2) : (3 * $number + 1);
+      $count++;
+    }
+    return $count;
+  }

exercises/practice/collatz-conjecture/.meta/tests.toml

@@ -0,0 +1,38 @@
+# 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.
+
+[540a3d51-e7a6-47a5-92a3-4ad1838f0bfd]
+description = "zero steps for one"
+
+[3d76a0a6-ea84-444a-821a-f7857c2c1859]
+description = "divide if even"
+
+[754dea81-123c-429e-b8bc-db20b05a87b9]
+description = "even and odd steps"
+
+[ecfd0210-6f85-44f6-8280-f65534892ff6]
+description = "large number of even and odd steps"
+
+[7d4750e6-def9-4b86-aec7-9f7eb44f95a3]
+description = "zero is an error"
+include = false
+
+[2187673d-77d6-4543-975e-66df6c50e2da]
+description = "zero is an error"
+reimplements = "7d4750e6-def9-4b86-aec7-9f7eb44f95a3"
+
+[c6c795bf-a288-45e9-86a1-841359ad426d]
+description = "negative value is an error"
+include = false
+
+[ec11f479-56bc-47fd-a434-bcd7a31a7a2e]
+description = "negative value is an error"
+reimplements = "c6c795bf-a288-45e9-86a1-841359ad426d"

exercises/practice/collatz-conjecture/lib/CollatzConjecture.pm

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

exercises/practice/collatz-conjecture/t/collatz-conjecture.t

@@ -0,0 +1,45 @@
+#!/usr/bin/env perl
+use Test2::V0;
+
+use FindBin qw<$Bin>;
+use lib "$Bin/../lib", "$Bin/../local/lib/perl5";
+
+use CollatzConjecture qw<steps>;
+
+is( # begin: 540a3d51-e7a6-47a5-92a3-4ad1838f0bfd
+    steps(1),
+    0,
+    "zero steps for one",
+); # end: 540a3d51-e7a6-47a5-92a3-4ad1838f0bfd
+
+is( # begin: 3d76a0a6-ea84-444a-821a-f7857c2c1859
+    steps(16),
+    4,
+    "divide if even",
+); # end: 3d76a0a6-ea84-444a-821a-f7857c2c1859
+
+is( # begin: 754dea81-123c-429e-b8bc-db20b05a87b9
+    steps(12),
+    9,
+    "even and odd steps",
+); # end: 754dea81-123c-429e-b8bc-db20b05a87b9
+
+is( # begin: ecfd0210-6f85-44f6-8280-f65534892ff6
+    steps(1000000),
+    152,
+    "large number of even and odd steps",
+); # end: ecfd0210-6f85-44f6-8280-f65534892ff6
+
+like( # begin: 2187673d-77d6-4543-975e-66df6c50e2da
+    dies( sub { steps(0) } ),
+    qr/Only positive integers are allowed/,
+    "zero is an error",
+); # end: 2187673d-77d6-4543-975e-66df6c50e2da
+
+like( # begin: ec11f479-56bc-47fd-a434-bcd7a31a7a2e
+    dies( sub { steps(-15) } ),
+    qr/Only positive integers are allowed/,
+    "negative value is an error",
+); # end: ec11f479-56bc-47fd-a434-bcd7a31a7a2e
+
+done_testing;