From 4b25a6b1c643b8377797bff7cd5a55f6d4df0553 Mon Sep 17 00:00:00 2001
From: Fabio Scotto di Santolo <fabio.scottodisantolo@gmail.com>
Date: Thu, 5 Jan 2023 15:13:07 +0100
Subject: [PATCH] Implemented linked list data structure

---
 pkg/collection/linked_list.go      | 226 ++++++++++++++++++++++++
 pkg/collection/linked_list_test.go | 273 +++++++++++++++++++++++++++++
 2 files changed, 499 insertions(+)
 create mode 100644 pkg/collection/linked_list.go
 create mode 100644 pkg/collection/linked_list_test.go

diff --git a/pkg/collection/linked_list.go b/pkg/collection/linked_list.go
new file mode 100644
index 0000000..b7b65c6
--- /dev/null
+++ b/pkg/collection/linked_list.go
@@ -0,0 +1,226 @@
+package collection
+
+import (
+	"fmt"
+	"log"
+	"strings"
+)
+
+var (
+	ErrPositionNegative = fmt.Errorf("position can not be negative")
+	ErrEmptyList        = fmt.Errorf("no nodes in list")
+	ErrNodeNotFound     = fmt.Errorf("node not found")
+)
+
+type ErrIndexOutOfBound struct {
+	index int
+	size  int
+}
+
+func (e ErrIndexOutOfBound) Error() string {
+	return fmt.Sprintf("index %d out of bound from range %d and %d", e.index, 0, e.size-1)
+}
+
+type node[E any] struct {
+	value E
+	prev  *node[E]
+	next  *node[E]
+}
+
+type listIterator[E any] struct {
+	currentNode  *node[E]
+	currentIndex int
+}
+
+func (it *listIterator[E]) HasNext() bool {
+	return it.currentNode != nil
+}
+
+func (it *listIterator[E]) Next() E {
+	curr := it.currentNode
+	it.currentNode = curr.next
+	it.currentIndex++
+	return curr.value
+}
+
+func (it *listIterator[E]) NextWithIndex() (int, E) {
+	curr := it.currentNode
+	index := it.currentIndex
+	it.currentNode = curr.next
+	it.currentIndex++
+	return index, curr.value
+}
+
+type emptyListIterator[E any] struct{}
+
+func (it *emptyListIterator[E]) HasNext() bool {
+	return false
+}
+
+func (it *emptyListIterator[E]) Next() E {
+	return *new(E)
+}
+
+func (it *emptyListIterator[E]) NextWithIndex() (int, E) {
+	return 0, *new(E)
+}
+
+type LinkedList[E any] struct {
+	head *node[E]
+	size int
+}
+
+func (l *LinkedList[E]) Iterator() Iterator[E] {
+	if l.Empty() {
+		return &emptyListIterator[E]{}
+	}
+	return &listIterator[E]{l.head, 0}
+}
+
+func (l *LinkedList[E]) Empty() bool {
+	return l.head == nil
+}
+
+func (l *LinkedList[E]) Size() int {
+	return l.size
+}
+
+func (l *LinkedList[E]) Back() (E, error) {
+	return l.GetAt(l.size - 1)
+}
+
+func (l *LinkedList[E]) Front() (E, error) {
+	return l.GetAt(0)
+}
+
+func (l *LinkedList[E]) GetAt(pos int) (E, error) {
+	node, err := l.findNode(pos)
+	if err != nil {
+		return *new(E), err
+	}
+	return node.value, nil
+}
+
+// findNode returns node at given position from linked list
+func (l *LinkedList[E]) findNode(pos int) (*node[E], error) {
+	if l.Empty() {
+		return nil, ErrEmptyList
+	}
+
+	ptr := l.head
+	if pos < 0 {
+		return nil, ErrPositionNegative
+	}
+
+	if pos > (l.size - 1) {
+		return nil, ErrIndexOutOfBound{pos, l.size}
+	}
+
+	for i := 0; i < pos; i++ {
+		ptr = ptr.next
+	}
+
+	return ptr, nil
+}
+
+func (l *LinkedList[E]) PushFront(item E) {
+	l.PushAt(item, 0)
+}
+
+func (l *LinkedList[E]) PushBack(item E) {
+	l.PushAt(item, l.size)
+}
+
+// PushAt inserts new node at given position
+func (l *LinkedList[E]) PushAt(item E, pos int) {
+	// create a new node
+	newNode := node[E]{value: item}
+
+	// validate the position
+	if pos < 0 {
+		return
+	}
+
+	if pos == 0 {
+		oldNode := l.head
+		newNode.next = oldNode
+		l.head = &newNode
+		if oldNode != nil {
+			oldNode.prev = l.head
+		}
+		l.size++
+		return
+	}
+	if pos > l.size {
+		return
+	}
+	n, _ := l.findNode(pos)
+	newNode.next = n
+	var prevNode *node[E]
+	if n != nil {
+		prevNode = n.prev
+	} else {
+		prevNode, _ = l.findNode(pos - 1)
+	}
+	prevNode.next = &newNode
+	newNode.prev = prevNode
+	l.size++
+}
+
+// DeleteAt deletes node at given position from linked list
+func (l *LinkedList[E]) DeleteAt(pos int) error {
+	// validate the position
+	if pos < 0 {
+		log.Println("position can not be negative")
+		return ErrPositionNegative
+	}
+
+	if l.size == 0 {
+		log.Println("no nodes in list")
+		return ErrEmptyList
+	}
+
+	if pos == 0 {
+		// For first position not exists prev node
+		myNode, err := l.findNode(pos)
+		if err != nil {
+			return err
+		}
+		l.head = myNode.next
+		l.head.prev = nil
+	} else {
+		prevNode, _ := l.findNode(pos - 1)
+		if prevNode == nil {
+			log.Println("node not found")
+			return ErrNodeNotFound
+		}
+		myNode, err := l.findNode(pos)
+		if err != nil {
+			return err
+		}
+		prevNode.next = myNode.next
+		if myNode.next != nil {
+			myNode.next.prev = prevNode
+		}
+	}
+
+	l.size--
+	return nil
+}
+
+func (l *LinkedList[E]) String() string {
+	var sb strings.Builder
+	sb.WriteString("[")
+	for i := 0; i < l.Size(); i++ {
+		var s string
+		item, _ := l.GetAt(i)
+		if i >= l.Size()-1 {
+			s = fmt.Sprintf("%v", item)
+		} else {
+			s = fmt.Sprintf("%v, ", item)
+		}
+		sb.WriteString(s)
+	}
+	sb.WriteString("]")
+	return sb.String()
+}
diff --git a/pkg/collection/linked_list_test.go b/pkg/collection/linked_list_test.go
new file mode 100644
index 0000000..521e81f
--- /dev/null
+++ b/pkg/collection/linked_list_test.go
@@ -0,0 +1,273 @@
+package collection
+
+import (
+	"testing"
+)
+
+func TestLinkedList_Empty(t *testing.T) {
+	useCases := []struct {
+		description string
+		list        *LinkedList[int]
+		want        bool
+	}{
+		{description: "no items in list", list: newList(), want: true},
+		{description: "one item in list", list: newList(1), want: false},
+		{description: "more items in list", list: newList(1, 2, 3), want: false},
+	}
+
+	for _, tt := range useCases {
+		result := tt.list.Empty()
+		if result != tt.want {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestLinkedList_Size(t *testing.T) {
+	useCases := []struct {
+		description string
+		list        *LinkedList[int]
+		want        int
+	}{
+		{description: "no items in list", list: newList(), want: 0},
+		{description: "one item in list", list: newList(1), want: 1},
+		{description: "more items in list", list: newList(1, 2, 3), want: 3},
+	}
+
+	for _, tt := range useCases {
+		result := tt.list.Size()
+		if result != tt.want {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestLinkedList_GetAt(t *testing.T) {
+	useCases := []struct {
+		description string
+		list        *LinkedList[int]
+		pos         int
+		err         error
+		want        int
+	}{
+		{description: "get first item", list: newList(1, 2, 3), pos: 0, want: 1, err: nil},
+		{description: "get middle item", list: newList(1, 2, 3), pos: 1, want: 2, err: nil},
+		{description: "get last item", list: newList(1, 2, 3), pos: 2, want: 3, err: nil},
+		{description: "get last item", list: newList(1, 2, 3), pos: 2, want: 3, err: nil},
+		{description: "no items in list return zero value of the type", list: newList(), pos: 0, want: 0, err: ErrEmptyList},
+		{description: "get item with negative position", list: newList(1, 2, 3), pos: -1, want: 0, err: ErrPositionNegative},
+		{description: "get item with index out of bound", list: newList(1, 2, 3), pos: 4, want: 0, err: ErrIndexOutOfBound{4, 3}},
+	}
+
+	for _, tt := range useCases {
+		result, err := tt.list.GetAt(tt.pos)
+		if result != tt.want && err != tt.err {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestLinkedList_Back(t *testing.T) {
+	useCases := []struct {
+		description string
+		list        *LinkedList[int]
+		err         error
+		want        int
+	}{
+		{description: "no items in list return zero value of the type", list: newList(), want: 0, err: ErrEmptyList},
+		{description: "singleton list return first element", list: newList(1), want: 1},
+		{description: "get last item", list: newList(1, 2, 3), want: 3},
+	}
+
+	for _, tt := range useCases {
+		result, err := tt.list.Back()
+		if result != tt.want && err != tt.err {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestLinkedList_Front(t *testing.T) {
+	useCases := []struct {
+		description string
+		list        *LinkedList[int]
+		err         error
+		want        int
+	}{
+		{description: "no items in list return zero value of the type", list: newList(), want: 0, err: ErrEmptyList},
+		{description: "singleton list return first element", list: newList(1), want: 1},
+		{description: "get first item", list: newList(1, 2, 3), want: 1},
+	}
+
+	for _, tt := range useCases {
+		result, err := tt.list.Front()
+		if result != tt.want && err != tt.err {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestLinkedList_PushAt(t *testing.T) {
+	useCases := []struct {
+		description string
+		original    *LinkedList[int]
+		modified    *LinkedList[int]
+		pos         int
+		item        int
+	}{
+		{description: "add item in first position in empty list",
+			original: newList(),
+			modified: newList(1),
+			pos:      0,
+			item:     1},
+		{description: "add item in first position in full list",
+			original: newList(1, 2, 3),
+			modified: newList(0, 1, 2, 3),
+			pos:      0,
+			item:     0},
+		{description: "add item in middle position in full list",
+			original: newList(1, 2, 3),
+			modified: newList(1, 2, 0, 3),
+			pos:      2,
+			item:     0},
+		{description: "add item in last position in full list",
+			original: newList(1, 2, 3),
+			modified: newList(1, 2, 3, 0),
+			pos:      3,
+			item:     0},
+	}
+
+	for _, tt := range useCases {
+		tt.original.PushAt(tt.item, tt.pos)
+		if !compareLists(tt.original, tt.modified) {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.modified, tt.original)
+		}
+	}
+}
+
+func TestLinkedList_PushBack(t *testing.T) {
+	useCases := []struct {
+		description string
+		original    *LinkedList[int]
+		modified    *LinkedList[int]
+		pos         int
+		item        int
+	}{
+		{description: "add item in first position in empty list",
+			original: newList(),
+			modified: newList(1),
+			item:     1},
+		{description: "add item in singleton list",
+			original: newList(1),
+			modified: newList(1, 0),
+			item:     0},
+		{description: "add item in full list",
+			original: newList(1, 2, 3),
+			modified: newList(1, 2, 3, 0),
+			item:     0},
+	}
+
+	for _, tt := range useCases {
+		tt.original.PushBack(tt.item)
+		if !compareLists(tt.original, tt.modified) {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.modified, tt.original)
+		}
+	}
+}
+
+func TestLinkedList_PushFront(t *testing.T) {
+	useCases := []struct {
+		description string
+		original    *LinkedList[int]
+		modified    *LinkedList[int]
+		pos         int
+		item        int
+	}{
+		{description: "add item in first position in empty list",
+			original: newList(),
+			modified: newList(1),
+			item:     1},
+		{description: "add item in singleton list",
+			original: newList(1),
+			modified: newList(0, 1),
+			item:     0},
+		{description: "add item in full list",
+			original: newList(1, 2, 3),
+			modified: newList(0, 1, 2, 3),
+			item:     0},
+	}
+
+	for _, tt := range useCases {
+		tt.original.PushFront(tt.item)
+		if !compareLists(tt.original, tt.modified) {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.modified, tt.original)
+		}
+	}
+}
+
+func TestLinkedList_DeleteAt(t *testing.T) {
+	useCases := []struct {
+		description string
+		original    *LinkedList[int]
+		modified    *LinkedList[int]
+		pos         int
+		err         error
+	}{
+		{description: "delete item with negative position",
+			original: newList(),
+			modified: nil,
+			pos:      -1,
+			err:      ErrPositionNegative},
+		{description: "delete item in empty list",
+			original: newList(),
+			modified: nil,
+			pos:      0,
+			err:      ErrEmptyList},
+		{description: "delete item in position not found",
+			original: newList(1, 2, 3),
+			modified: newList(),
+			pos:      5,
+			err:      ErrNodeNotFound},
+		{description: "delete item in first position",
+			original: newList(1, 2, 3),
+			modified: newList(2, 3),
+			pos:      0,
+			err:      nil},
+		{description: "delete item in middle position",
+			original: newList(1, 2, 3),
+			modified: newList(1, 3),
+			pos:      1,
+			err:      nil},
+		{description: "delete item in last position",
+			original: newList(1, 2, 3),
+			modified: newList(1, 2),
+			pos:      2,
+			err:      nil},
+	}
+
+	for _, tt := range useCases {
+		err := tt.original.DeleteAt(tt.pos)
+		if !compareLists(tt.original, tt.modified) && err != tt.err {
+			t.Errorf("test: %s want %v got %v", tt.description, tt.modified, tt.original)
+		}
+	}
+}
+
+func newList(items ...int) *LinkedList[int] {
+	lst := &LinkedList[int]{}
+	for _, item := range items {
+		lst.PushBack(item)
+	}
+	return lst
+}
+
+func compareLists(lst1, lst2 *LinkedList[int]) bool {
+	for it := lst1.Iterator(); it.HasNext(); {
+		i, item1 := it.NextWithIndex()
+		item2, _ := lst2.GetAt(i)
+		if item1 != item2 {
+			return false
+		}
+	}
+	return true
+}