From 88909faafccc102ec8a3127e4526ef8118a267d4 Mon Sep 17 00:00:00 2001
From: Glenn Jackman <glenn.jackman@gmail.com>
Date: Wed, 24 Dec 2025 18:54:48 -0500
Subject: [PATCH] linked-list

---
 config.json                                   |   8 +
 exercises/practice/linked-list/.busted        |   5 +
 .../linked-list/.docs/instructions.md         |  26 +++
 .../linked-list/.docs/introduction.md         |   6 +
 .../practice/linked-list/.meta/config.json    |  18 ++
 .../practice/linked-list/.meta/example.moon   |  68 ++++++++
 .../linked-list/.meta/spec_generator.moon     |  17 ++
 .../practice/linked-list/.meta/tests.toml     |  67 ++++++++
 .../practice/linked-list/linked_list.moon     |  21 +++
 .../linked-list/linked_list_spec.moon         | 157 ++++++++++++++++++
 10 files changed, 393 insertions(+)
 create mode 100644 exercises/practice/linked-list/.busted
 create mode 100644 exercises/practice/linked-list/.docs/instructions.md
 create mode 100644 exercises/practice/linked-list/.docs/introduction.md
 create mode 100644 exercises/practice/linked-list/.meta/config.json
 create mode 100644 exercises/practice/linked-list/.meta/example.moon
 create mode 100644 exercises/practice/linked-list/.meta/spec_generator.moon
 create mode 100644 exercises/practice/linked-list/.meta/tests.toml
 create mode 100644 exercises/practice/linked-list/linked_list.moon
 create mode 100644 exercises/practice/linked-list/linked_list_spec.moon

diff --git a/config.json b/config.json
index 2f3e073..e8f1b20 100644
--- a/config.json
+++ b/config.json
@@ -350,6 +350,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "linked-list",
+        "name": "Linked List",
+        "uuid": "e4d7413a-6429-4d6e-bcfd-580c9a449d4e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },
diff --git a/exercises/practice/linked-list/.busted b/exercises/practice/linked-list/.busted
new file mode 100644
index 0000000..86b84e7
--- /dev/null
+++ b/exercises/practice/linked-list/.busted
@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}
diff --git a/exercises/practice/linked-list/.docs/instructions.md b/exercises/practice/linked-list/.docs/instructions.md
new file mode 100644
index 0000000..edf4055
--- /dev/null
+++ b/exercises/practice/linked-list/.docs/instructions.md
@@ -0,0 +1,26 @@
+# Instructions
+
+Your team has decided to use a doubly linked list to represent each train route in the schedule.
+Each station along the train's route will be represented by a node in the linked list.
+
+You don't need to worry about arrival and departure times at the stations.
+Each station will simply be represented by a number.
+
+Routes can be extended, adding stations to the beginning or end of a route.
+They can also be shortened by removing stations from the beginning or the end of a route.
+
+Sometimes a station gets closed down, and in that case the station needs to be removed from the route, even if it is not at the beginning or end of the route.
+
+The size of a route is measured not by how far the train travels, but by how many stations it stops at.
+
+~~~~exercism/note
+The linked list is a fundamental data structure in computer science, often used in the implementation of other data structures.
+As the name suggests, it is a list of nodes that are linked together.
+It is a list of "nodes", where each node links to its neighbor or neighbors.
+In a **singly linked list** each node links only to the node that follows it.
+In a **doubly linked list** each node links to both the node that comes before, as well as the node that comes after.
+
+If you want to dig deeper into linked lists, check out [this article][intro-linked-list] that explains it using nice drawings.
+
+[intro-linked-list]: https://medium.com/basecs/whats-a-linked-list-anyway-part-1-d8b7e6508b9d
+~~~~
diff --git a/exercises/practice/linked-list/.docs/introduction.md b/exercises/practice/linked-list/.docs/introduction.md
new file mode 100644
index 0000000..6e83ae7
--- /dev/null
+++ b/exercises/practice/linked-list/.docs/introduction.md
@@ -0,0 +1,6 @@
+# Introduction
+
+You are working on a project to develop a train scheduling system for a busy railway network.
+
+You've been asked to develop a prototype for the train routes in the scheduling system.
+Each route consists of a sequence of train stations that a given train stops at.
diff --git a/exercises/practice/linked-list/.meta/config.json b/exercises/practice/linked-list/.meta/config.json
new file mode 100644
index 0000000..dfd22fb
--- /dev/null
+++ b/exercises/practice/linked-list/.meta/config.json
@@ -0,0 +1,18 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "linked_list.moon"
+    ],
+    "test": [
+      "linked_list_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "blurb": "Implement a doubly linked list.",
+  "source": "Classic computer science topic"
+}
diff --git a/exercises/practice/linked-list/.meta/example.moon b/exercises/practice/linked-list/.meta/example.moon
new file mode 100644
index 0000000..213dec2
--- /dev/null
+++ b/exercises/practice/linked-list/.meta/example.moon
@@ -0,0 +1,68 @@
+class LinkedList
+  new: (@head = nil, @tail = nil) =>
+
+  push: (value) =>
+    node = {:value, next: nil, prev: nil}
+    if @tail
+      @tail.next = node
+      node.prev = @tail
+    else
+      @head = node
+    @tail = node
+
+  unshift: (value) =>
+    node = {:value, next: nil, prev: nil}
+    if @head
+      @head.prev = node
+      node.next = @head
+    else
+      @tail = node
+    @head = node
+
+  pop: =>
+    return unless @tail
+    value = @tail.value
+    if @head == @tail
+      @head, @tail = nil, nil
+    else
+      @tail.prev.next = nil
+      @tail = @tail.prev
+    value
+
+  shift: =>
+    return unless @head
+    value = @head.value
+    if @head == @tail
+      @head, @tail = nil, nil
+    else
+      @head.next.prev = nil
+      @head = @head.next
+    value
+
+  count: =>
+    n = 0
+    node = @head
+    while node != nil
+      n += 1
+      node = node.next
+    n
+
+  delete: (value) =>
+    node = @head
+    while node != nil
+      if node.value == value
+        if node.prev and node.next
+          node.prev.next = node.next
+          node.next.prev = node.prev
+          node = nil
+        elseif node.next
+          -- this is the head
+          @shift!
+        elseif node.prev
+          -- this is the tail
+          @pop!
+        else
+          @head, @tail = nil, nil
+        break
+      -- end if
+      node = node.next
diff --git a/exercises/practice/linked-list/.meta/spec_generator.moon b/exercises/practice/linked-list/.meta/spec_generator.moon
new file mode 100644
index 0000000..f82bb6e
--- /dev/null
+++ b/exercises/practice/linked-list/.meta/spec_generator.moon
@@ -0,0 +1,17 @@
+{
+  module_name: 'LinkedList',
+
+  generate_test: (case, level) ->
+    lines = {
+      "list = LinkedList!",
+    }
+    for op in *case.input.operations
+      if op.value
+        table.insert lines, "list\\#{op.operation} #{op.value}"
+      elseif op.expected
+        table.insert lines, "assert.are.equal #{op.expected}, list\\#{op.operation}!"
+      else
+        table.insert lines, "list\\#{op.operation}!"
+
+    table.concat [indent line, level for line in *lines], '\n'
+}
diff --git a/exercises/practice/linked-list/.meta/tests.toml b/exercises/practice/linked-list/.meta/tests.toml
new file mode 100644
index 0000000..96906d2
--- /dev/null
+++ b/exercises/practice/linked-list/.meta/tests.toml
@@ -0,0 +1,67 @@
+# 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.
+
+[7f7e3987-b954-41b8-8084-99beca08752c]
+description = "pop gets element from the list"
+
+[c3f67e5d-cfa2-4c3e-a18f-7ce999c3c885]
+description = "push/pop respectively add/remove at the end of the list"
+
+[00ea24ce-4f5c-4432-abb4-cc6e85462657]
+description = "shift gets an element from the list"
+
+[37962ee0-3324-4a29-b588-5a4c861e6564]
+description = "shift gets first element from the list"
+
+[30a3586b-e9dc-43fb-9a73-2770cec2c718]
+description = "unshift adds element at start of the list"
+
+[042f71e4-a8a7-4cf0-8953-7e4f3a21c42d]
+description = "pop, push, shift, and unshift can be used in any order"
+
+[88f65c0c-4532-4093-8295-2384fb2f37df]
+description = "count an empty list"
+
+[fc055689-5cbe-4cd9-b994-02e2abbb40a5]
+description = "count a list with items"
+
+[8272cef5-130d-40ea-b7f6-5ffd0790d650]
+description = "count is correct after mutation"
+
+[229b8f7a-bd8a-4798-b64f-0dc0bb356d95]
+description = "popping to empty doesn't break the list"
+
+[4e1948b4-514e-424b-a3cf-a1ebbfa2d1ad]
+description = "shifting to empty doesn't break the list"
+
+[e8f7c600-d597-4f79-949d-8ad8bae895a6]
+description = "deletes the only element"
+
+[fd65e422-51f3-45c0-9fd0-c33da638f89b]
+description = "deletes the element with the specified value from the list"
+
+[59db191a-b17f-4ab7-9c5c-60711ec1d013]
+description = "deletes the element with the specified value from the list, re-assigns tail"
+
+[58242222-5d39-415b-951d-8128247f8993]
+description = "deletes the element with the specified value from the list, re-assigns head"
+
+[ee3729ee-3405-4bd2-9bad-de0d4aa5d647]
+description = "deletes the first of two elements"
+
+[47e3b3b4-b82c-4c23-8c1a-ceb9b17cb9fb]
+description = "deletes the second of two elements"
+
+[7b420958-f285-4922-b8f9-10d9dcab5179]
+description = "delete does not modify the list if the element is not found"
+
+[7e04828f-6082-44e3-a059-201c63252a76]
+description = "deletes only the first occurrence"
diff --git a/exercises/practice/linked-list/linked_list.moon b/exercises/practice/linked-list/linked_list.moon
new file mode 100644
index 0000000..b8a02d0
--- /dev/null
+++ b/exercises/practice/linked-list/linked_list.moon
@@ -0,0 +1,21 @@
+class LinkedList
+  new: (...) =>
+    error 'Implement the constructor'
+
+  push: (value) =>
+    error 'Implement the push method'
+
+  unshift: (value) =>
+    error 'Implement the unshift method'
+
+  pop: =>
+    error 'Implement the pop method'
+
+  shift: =>
+    error 'Implement the shift method'
+
+  count: =>
+    error 'Implement the count method'
+
+  delete: (value) =>
+    error 'Implement the delete method'
diff --git a/exercises/practice/linked-list/linked_list_spec.moon b/exercises/practice/linked-list/linked_list_spec.moon
new file mode 100644
index 0000000..6333dfb
--- /dev/null
+++ b/exercises/practice/linked-list/linked_list_spec.moon
@@ -0,0 +1,157 @@
+LinkedList = require 'linked_list'
+
+describe 'linked-list', ->
+  it 'pop gets element from the list', ->
+    list = LinkedList!
+    list\push 7
+    assert.are.equal 7, list\pop!
+
+  pending 'push/pop respectively add/remove at the end of the list', ->
+    list = LinkedList!
+    list\push 11
+    list\push 13
+    assert.are.equal 13, list\pop!
+    assert.are.equal 11, list\pop!
+
+  pending 'shift gets an element from the list', ->
+    list = LinkedList!
+    list\push 17
+    assert.are.equal 17, list\shift!
+
+  pending 'shift gets first element from the list', ->
+    list = LinkedList!
+    list\push 23
+    list\push 5
+    assert.are.equal 23, list\shift!
+    assert.are.equal 5, list\shift!
+
+  pending 'unshift adds element at start of the list', ->
+    list = LinkedList!
+    list\unshift 23
+    list\unshift 5
+    assert.are.equal 5, list\shift!
+    assert.are.equal 23, list\shift!
+
+  pending 'pop, push, shift, and unshift can be used in any order', ->
+    list = LinkedList!
+    list\push 1
+    list\push 2
+    assert.are.equal 2, list\pop!
+    list\push 3
+    assert.are.equal 1, list\shift!
+    list\unshift 4
+    list\push 5
+    assert.are.equal 4, list\shift!
+    assert.are.equal 5, list\pop!
+    assert.are.equal 3, list\shift!
+
+  pending 'count an empty list', ->
+    list = LinkedList!
+    assert.are.equal 0, list\count!
+
+  pending 'count a list with items', ->
+    list = LinkedList!
+    list\push 37
+    list\push 1
+    assert.are.equal 2, list\count!
+
+  pending 'count is correct after mutation', ->
+    list = LinkedList!
+    list\push 31
+    assert.are.equal 1, list\count!
+    list\unshift 43
+    assert.are.equal 2, list\count!
+    list\shift!
+    assert.are.equal 1, list\count!
+    list\pop!
+    assert.are.equal 0, list\count!
+
+  pending "popping to empty doesn't break the list", ->
+    list = LinkedList!
+    list\push 41
+    list\push 59
+    list\pop!
+    list\pop!
+    list\push 47
+    assert.are.equal 1, list\count!
+    assert.are.equal 47, list\pop!
+
+  pending "shifting to empty doesn't break the list", ->
+    list = LinkedList!
+    list\push 41
+    list\push 59
+    list\shift!
+    list\shift!
+    list\push 47
+    assert.are.equal 1, list\count!
+    assert.are.equal 47, list\shift!
+
+  pending 'deletes the only element', ->
+    list = LinkedList!
+    list\push 61
+    list\delete 61
+    assert.are.equal 0, list\count!
+
+  pending 'deletes the element with the specified value from the list', ->
+    list = LinkedList!
+    list\push 71
+    list\push 83
+    list\push 79
+    list\delete 83
+    assert.are.equal 2, list\count!
+    assert.are.equal 79, list\pop!
+    assert.are.equal 71, list\shift!
+
+  pending 'deletes the element with the specified value from the list, re-assigns tail', ->
+    list = LinkedList!
+    list\push 71
+    list\push 83
+    list\push 79
+    list\delete 83
+    assert.are.equal 2, list\count!
+    assert.are.equal 79, list\pop!
+    assert.are.equal 71, list\pop!
+
+  pending 'deletes the element with the specified value from the list, re-assigns head', ->
+    list = LinkedList!
+    list\push 71
+    list\push 83
+    list\push 79
+    list\delete 83
+    assert.are.equal 2, list\count!
+    assert.are.equal 71, list\shift!
+    assert.are.equal 79, list\shift!
+
+  pending 'deletes the first of two elements', ->
+    list = LinkedList!
+    list\push 97
+    list\push 101
+    list\delete 97
+    assert.are.equal 1, list\count!
+    assert.are.equal 101, list\pop!
+
+  pending 'deletes the second of two elements', ->
+    list = LinkedList!
+    list\push 97
+    list\push 101
+    list\delete 101
+    assert.are.equal 1, list\count!
+    assert.are.equal 97, list\pop!
+
+  pending 'delete does not modify the list if the element is not found', ->
+    list = LinkedList!
+    list\push 89
+    list\delete 103
+    assert.are.equal 1, list\count!
+
+  pending 'deletes only the first occurrence', ->
+    list = LinkedList!
+    list\push 73
+    list\push 9
+    list\push 9
+    list\push 107
+    list\delete 9
+    assert.are.equal 3, list\count!
+    assert.are.equal 107, list\pop!
+    assert.are.equal 9, list\pop!
+    assert.are.equal 73, list\pop!