Collatz conjecture

.gitignore

@@ -10,3 +10,4 @@ bin/configlet
 .psc-ide-port
 
 .merlin
+_opam

bin/add-practice-exercise

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+
+# Synopsis:
+# Scaffold the files for a new practice exercise.
+# After creating the exercise, follow the instructions in the output.
+
+# Example:
+# bin/add-practice-exercise two-fer
+
+# Example with difficulty:
+# bin/add-practice-exercise -d 5 two-fer
+
+# Example with author and difficulty:
+# bin/add-practice-exercise -a foo -d 3 two-fer
+
+set -euo pipefail
+scriptname=$0
+
+help_and_exit() {
+    echo >&2 "Scaffold the files for a new practice exercise."
+    echo >&2 "Usage: ${scriptname} [-h] [-a author] [-d difficulty] <exercise-slug>"
+    echo >&2 "Where: author is the GitHub username of the exercise creator."
+    echo >&2 "Where: difficulty is between 1 (easiest) to 10 (hardest)."
+    exit 1
+}
+
+die() { echo >&2 "$*"; exit 1; }
+
+required_tool() {
+    command -v "${1}" >/dev/null 2>&1 ||
+        die "${1} is required but not installed. Please install it and make sure it's in your PATH."
+}
+
+require_files_template() {
+    jq -e --arg key "${1}" '.files[$key] | length > 0' config.json > /dev/null ||
+        die "The '.files.${1}' array in the 'config.json' file is empty. Please add at least one file. See https://exercism.org/docs/building/tracks/config-json#h-files for more information."
+}
+
+required_tool jq
+
+require_files_template "solution"
+require_files_template "test"
+require_files_template "example"
+
+[[ -f ./bin/fetch-configlet ]] || die "Run this script from the repo's root directory."
+
+author=''
+difficulty='1'
+while getopts :ha:d: opt; do
+    case $opt in
+        h) help_and_exit ;;
+        a) author=$OPTARG ;;
+        d) difficulty=$OPTARG ;;
+        ?) echo >&2 "Unknown option: -$OPTARG"; help_and_exit ;;
+    esac
+done
+shift "$((OPTIND - 1))"
+
+(( $# >= 1 )) || help_and_exit
+
+slug="${1}"
+
+if [[ -z "${author}" ]]; then
+    read -rp 'Your GitHub username: ' author
+fi
+
+./bin/fetch-configlet
+./bin/configlet create --practice-exercise "${slug}" --author "${author}" --difficulty "${difficulty}"
+
+exercise_dir="exercises/practice/${slug}"
+files=$(jq -r --arg dir "${exercise_dir}" '.files | to_entries | map({key: .key, value: (.value | map("'"'"'" + $dir + "/" + . + "'"'"'") | join(" and "))}) | from_entries' "${exercise_dir}/.meta/config.json")
+
+cat << NEXT_STEPS
+
+Your next steps are:
+- Create the test suite in $(jq -r '.test' <<< "${files}")
+  - The tests should be based on the canonical data at 'https://github.com/exercism/problem-specifications/blob/main/exercises/${slug}/canonical-data.json'
+  - Any test cases you don't implement, mark them in 'exercises/practice/${slug}/.meta/tests.toml' with "include = false"
+- Create the example solution in $(jq -r '.example' <<< "${files}")
+- Verify the example solution passes the tests by running 'bin/verify-exercises ${slug}'
+- Create the stub solution in $(jq -r '.solution' <<< "${files}")
+- Update the 'difficulty' value for the exercise's entry in the 'config.json' file in the repo's root
+- Validate CI using 'bin/configlet lint' and 'bin/configlet fmt'
+NEXT_STEPS

config.json

@@ -582,6 +582,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 3
+      },
+      {
+        "slug": "collatz-conjecture",
+        "name": "Collatz Conjecture",
+        "uuid": "eedc9471-326b-4498-b763-5b1c8eedca88",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

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

@@ -0,0 +1,3 @@
+# Instructions
+
+Given a positive integer, return the number of steps it takes to reach 1 according to the rules of the Collatz Conjecture.

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

@@ -0,0 +1,28 @@
+# Introduction
+
+One evening, you stumbled upon an old notebook filled with cryptic scribbles, as though someone had been obsessively chasing an idea.
+On one page, a single question stood out: **Can every number find its way to 1?**
+It was tied to something called the **Collatz Conjecture**, a puzzle that has baffled thinkers for decades.
+
+The rules were deceptively simple.
+Pick any positive integer.
+
+- If it's even, divide it by 2.
+- If it's odd, multiply it by 3 and add 1.
+
+Then, repeat these steps with the result, continuing indefinitely.
+
+Curious, you picked number 12 to test and began the journey:
+
+12 ➜ 6 ➜ 3 ➜ 10 ➜ 5 ➜ 16 ➜ 8 ➜ 4 ➜ 2 ➜ 1
+
+Counting from the second number (6), it took 9 steps to reach 1, and each time the rules repeated, the number kept changing.
+At first, the sequence seemed unpredictable — jumping up, down, and all over.
+Yet, the conjecture claims that no matter the starting number, we'll always end at 1.
+
+It was fascinating, but also puzzling.
+Why does this always seem to work?
+Could there be a number where the process breaks down, looping forever or escaping into infinity?
+The notebook suggested solving this could reveal something profound — and with it, fame, [fortune][collatz-prize], and a place in history awaits whoever could unlock its secrets.
+
+[collatz-prize]: https://mathprize.net/posts/collatz-conjecture/

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

@@ -0,0 +1,22 @@
+{
+  "authors": [
+    "therealowenrees"
+  ],
+  "files": {
+    "solution": [
+      "collatz_conjecture.ml"
+    ],
+    "test": [
+      "test.ml"
+    ],
+    "example": [
+      ".meta/example.ml"
+    ],
+    "editor": [
+      "collatz_conjecture.mli"
+    ]
+  },
+  "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Collatz_conjecture"
+}

exercises/practice/collatz-conjecture/.meta/example.ml

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+let collatz_conjecture n =
+    let rec aux n count =
+        match n with
+        | 1 -> Ok count
+        | _ -> 
+            (match n mod 2 with
+                | 0 -> aux (n / 2) (count + 1)
+                | _ -> aux (n * 3 + 1) (count + 1)
+            )
+    in
+    if n < 1 then Error "Only positive integers are allowed"
+    else aux n 0
+

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/Makefile

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+default: clean test
+
+test: 
+	dune runtest
+
+clean:
+	dune clean
+
+.PHONY: clean

exercises/practice/collatz-conjecture/collatz_conjecture.ml

@@ -0,0 +1,2 @@
+let collatz_conjecture _ = 
+  failwith "'collatz_conjecture' is missing"

exercises/practice/collatz-conjecture/collatz_conjecture.mli

@@ -0,0 +1 @@
+val collatz_conjecture : int -> (int, string) result

exercises/practice/collatz-conjecture/dune

@@ -0,0 +1,20 @@
+(executable
+ (name test)
+ (libraries base ounit2))
+
+(alias
+ (name runtest)
+ (deps
+  (:x test.exe))
+ (action
+  (run %{x})))
+
+(alias
+ (name buildtest)
+ (deps
+  (:x test.exe)))
+
+(env
+ (dev
+  (flags
+   (:standard -warn-error -A))))

exercises/practice/collatz-conjecture/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

exercises/practice/collatz-conjecture/test.ml

@@ -0,0 +1,20 @@
+open Base
+open OUnit2
+open Collatz_conjecture
+
+(* Assert Equals *)
+(* let ae exp got _test_ctxt =
+  assert_equal exp got *)
+let ae expected actual _ctx = assert_equal expected actual
+
+let tests = [
+  "zero steps for one" >:: ae (Ok 0) (collatz_conjecture 1);
+  "divide if even" >:: ae (Ok 4) (collatz_conjecture 16);
+  "even and odd steps" >:: ae (Ok 9) (collatz_conjecture 12);
+  "large number of even and odd steps" >:: ae (Ok 152) (collatz_conjecture 1000000);
+  "zero is an error" >:: ae (Error "Only positive integers are allowed") (collatz_conjecture 0);
+  "negative value is an error" >:: ae (Error "Only positive integers are allowed") (collatz_conjecture (-15));
+]
+
+let () =
+  run_test_tt_main ("collatz_conjecture tests" >::: tests)