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doublylinkedlist.go
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doublylinkedlist.go
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// Copyright (c) 2015, Emir Pasic. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package doublylinkedlist implements the doubly-linked list.
//
// Structure is not thread safe.
//
// Reference: https://en.wikipedia.org/wiki/List_%28abstract_data_type%29
package doublylinkedlist
import (
"fmt"
"slices"
"strings"
"github.com/emirpasic/gods/v2/lists"
"github.com/emirpasic/gods/v2/utils"
)
// Assert List implementation
var _ lists.List[any] = (*List[any])(nil)
// List holds the elements, where each element points to the next and previous element
type List[T comparable] struct {
first *element[T]
last *element[T]
size int
}
type element[T comparable] struct {
value T
prev *element[T]
next *element[T]
}
// New instantiates a new list and adds the passed values, if any, to the list
func New[T comparable](values ...T) *List[T] {
list := &List[T]{}
if len(values) > 0 {
list.Add(values...)
}
return list
}
// Add appends a value (one or more) at the end of the list (same as Append())
func (list *List[T]) Add(values ...T) {
for _, value := range values {
newElement := &element[T]{value: value, prev: list.last}
if list.size == 0 {
list.first = newElement
list.last = newElement
} else {
list.last.next = newElement
list.last = newElement
}
list.size++
}
}
// Append appends a value (one or more) at the end of the list (same as Add())
func (list *List[T]) Append(values ...T) {
list.Add(values...)
}
// Prepend prepends a values (or more)
func (list *List[T]) Prepend(values ...T) {
// in reverse to keep passed order i.e. ["c","d"] -> Prepend(["a","b"]) -> ["a","b","c",d"]
for v := len(values) - 1; v >= 0; v-- {
newElement := &element[T]{value: values[v], next: list.first}
if list.size == 0 {
list.first = newElement
list.last = newElement
} else {
list.first.prev = newElement
list.first = newElement
}
list.size++
}
}
// Get returns the element at index.
// Second return parameter is true if index is within bounds of the array and array is not empty, otherwise false.
func (list *List[T]) Get(index int) (T, bool) {
if !list.withinRange(index) {
var t T
return t, false
}
// determine traveral direction, last to first or first to last
if list.size-index < index {
element := list.last
for e := list.size - 1; e != index; e, element = e-1, element.prev {
}
return element.value, true
}
element := list.first
for e := 0; e != index; e, element = e+1, element.next {
}
return element.value, true
}
// Remove removes the element at the given index from the list.
func (list *List[T]) Remove(index int) {
if !list.withinRange(index) {
return
}
if list.size == 1 {
list.Clear()
return
}
var element *element[T]
// determine traversal direction, last to first or first to last
if list.size-index < index {
element = list.last
for e := list.size - 1; e != index; e, element = e-1, element.prev {
}
} else {
element = list.first
for e := 0; e != index; e, element = e+1, element.next {
}
}
if element == list.first {
list.first = element.next
}
if element == list.last {
list.last = element.prev
}
if element.prev != nil {
element.prev.next = element.next
}
if element.next != nil {
element.next.prev = element.prev
}
element = nil
list.size--
}
// Contains check if values (one or more) are present in the set.
// All values have to be present in the set for the method to return true.
// Performance time complexity of n^2.
// Returns true if no arguments are passed at all, i.e. set is always super-set of empty set.
func (list *List[T]) Contains(values ...T) bool {
if len(values) == 0 {
return true
}
if list.size == 0 {
return false
}
for _, value := range values {
found := false
for element := list.first; element != nil; element = element.next {
if element.value == value {
found = true
break
}
}
if !found {
return false
}
}
return true
}
// Values returns all elements in the list.
func (list *List[T]) Values() []T {
values := make([]T, list.size, list.size)
for e, element := 0, list.first; element != nil; e, element = e+1, element.next {
values[e] = element.value
}
return values
}
// IndexOf returns index of provided element
func (list *List[T]) IndexOf(value T) int {
if list.size == 0 {
return -1
}
for index, element := range list.Values() {
if element == value {
return index
}
}
return -1
}
// Empty returns true if list does not contain any elements.
func (list *List[T]) Empty() bool {
return list.size == 0
}
// Size returns number of elements within the list.
func (list *List[T]) Size() int {
return list.size
}
// Clear removes all elements from the list.
func (list *List[T]) Clear() {
list.size = 0
list.first = nil
list.last = nil
}
// Sort sorts values (in-place) using.
func (list *List[T]) Sort(comparator utils.Comparator[T]) {
if list.size < 2 {
return
}
values := list.Values()
slices.SortFunc(values, comparator)
list.Clear()
list.Add(values...)
}
// Swap swaps values of two elements at the given indices.
func (list *List[T]) Swap(i, j int) {
if list.withinRange(i) && list.withinRange(j) && i != j {
var element1, element2 *element[T]
for e, currentElement := 0, list.first; element1 == nil || element2 == nil; e, currentElement = e+1, currentElement.next {
switch e {
case i:
element1 = currentElement
case j:
element2 = currentElement
}
}
element1.value, element2.value = element2.value, element1.value
}
}
// Insert inserts values at specified index position shifting the value at that position (if any) and any subsequent elements to the right.
// Does not do anything if position is negative or bigger than list's size
// Note: position equal to list's size is valid, i.e. append.
func (list *List[T]) Insert(index int, values ...T) {
if !list.withinRange(index) {
// Append
if index == list.size {
list.Add(values...)
}
return
}
var beforeElement *element[T]
var foundElement *element[T]
// determine traversal direction, last to first or first to last
if list.size-index < index {
foundElement = list.last
beforeElement = list.last.prev
for e := list.size - 1; e != index; e, foundElement = e-1, foundElement.prev {
beforeElement = beforeElement.prev
}
} else {
foundElement = list.first
for e := 0; e != index; e, foundElement = e+1, foundElement.next {
beforeElement = foundElement
}
}
if foundElement == list.first {
oldNextElement := list.first
for i, value := range values {
newElement := &element[T]{value: value}
if i == 0 {
list.first = newElement
} else {
newElement.prev = beforeElement
beforeElement.next = newElement
}
beforeElement = newElement
}
oldNextElement.prev = beforeElement
beforeElement.next = oldNextElement
} else {
oldNextElement := beforeElement.next
for _, value := range values {
newElement := &element[T]{value: value}
newElement.prev = beforeElement
beforeElement.next = newElement
beforeElement = newElement
}
oldNextElement.prev = beforeElement
beforeElement.next = oldNextElement
}
list.size += len(values)
}
// Set value at specified index position
// Does not do anything if position is negative or bigger than list's size
// Note: position equal to list's size is valid, i.e. append.
func (list *List[T]) Set(index int, value T) {
if !list.withinRange(index) {
// Append
if index == list.size {
list.Add(value)
}
return
}
var foundElement *element[T]
// determine traversal direction, last to first or first to last
if list.size-index < index {
foundElement = list.last
for e := list.size - 1; e != index; {
fmt.Println("Set last", index, value, foundElement, foundElement.prev)
e, foundElement = e-1, foundElement.prev
}
} else {
foundElement = list.first
for e := 0; e != index; {
e, foundElement = e+1, foundElement.next
}
}
foundElement.value = value
}
// String returns a string representation of container
func (list *List[T]) String() string {
str := "DoublyLinkedList\n"
values := []string{}
for element := list.first; element != nil; element = element.next {
values = append(values, fmt.Sprintf("%v", element.value))
}
str += strings.Join(values, ", ")
return str
}
// Check that the index is within bounds of the list
func (list *List[T]) withinRange(index int) bool {
return index >= 0 && index < list.size
}