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//
// list
// ┌──────┐
// ┌──────────────┼─head │
// │ │ tail─┼──────────────┐
// │ └──────┘ │
// ▼ ▼
// item item item item
// ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐
// null ◀──┼─prev │◀───┼─prev │◀───┼─prev │◀───┼─prev │
// │ next─┼───▶│ next─┼───▶│ next─┼───▶│ next─┼──▶ null
// ├──────┤ ├──────┤ ├──────┤ ├──────┤
// │ data │ │ data │ │ data │ │ data │
// └──────┘ └──────┘ └──────┘ └──────┘
//
let releasedCursors = null;
export class List {
static createItem(data) {
return {
prev: null,
next: null,
data
};
}
constructor() {
this.head = null;
this.tail = null;
this.cursor = null;
}
createItem(data) {
return List.createItem(data);
}
// cursor helpers
allocateCursor(prev, next) {
let cursor;
if (releasedCursors !== null) {
cursor = releasedCursors;
releasedCursors = releasedCursors.cursor;
cursor.prev = prev;
cursor.next = next;
cursor.cursor = this.cursor;
} else {
cursor = {
prev,
next,
cursor: this.cursor
};
}
this.cursor = cursor;
return cursor;
}
releaseCursor() {
const { cursor } = this;
this.cursor = cursor.cursor;
cursor.prev = null;
cursor.next = null;
cursor.cursor = releasedCursors;
releasedCursors = cursor;
}
updateCursors(prevOld, prevNew, nextOld, nextNew) {
let { cursor } = this;
while (cursor !== null) {
if (cursor.prev === prevOld) {
cursor.prev = prevNew;
}
if (cursor.next === nextOld) {
cursor.next = nextNew;
}
cursor = cursor.cursor;
}
}
*[Symbol.iterator]() {
for (let cursor = this.head; cursor !== null; cursor = cursor.next) {
yield cursor.data;
}
}
// getters
get size() {
let size = 0;
for (let cursor = this.head; cursor !== null; cursor = cursor.next) {
size++;
}
return size;
}
get isEmpty() {
return this.head === null;
}
get first() {
return this.head && this.head.data;
}
get last() {
return this.tail && this.tail.data;
}
// convertors
fromArray(array) {
let cursor = null;
this.head = null;
for (let data of array) {
const item = List.createItem(data);
if (cursor !== null) {
cursor.next = item;
} else {
this.head = item;
}
item.prev = cursor;
cursor = item;
}
this.tail = cursor;
return this;
}
toArray() {
return [...this];
}
toJSON() {
return [...this];
}
// array-like methods
forEach(fn, thisArg = this) {
// push cursor
const cursor = this.allocateCursor(null, this.head);
while (cursor.next !== null) {
const item = cursor.next;
cursor.next = item.next;
fn.call(thisArg, item.data, item, this);
}
// pop cursor
this.releaseCursor();
}
forEachRight(fn, thisArg = this) {
// push cursor
const cursor = this.allocateCursor(this.tail, null);
while (cursor.prev !== null) {
const item = cursor.prev;
cursor.prev = item.prev;
fn.call(thisArg, item.data, item, this);
}
// pop cursor
this.releaseCursor();
}
reduce(fn, initialValue, thisArg = this) {
// push cursor
let cursor = this.allocateCursor(null, this.head);
let acc = initialValue;
let item;
while (cursor.next !== null) {
item = cursor.next;
cursor.next = item.next;
acc = fn.call(thisArg, acc, item.data, item, this);
}
// pop cursor
this.releaseCursor();
return acc;
}
reduceRight(fn, initialValue, thisArg = this) {
// push cursor
let cursor = this.allocateCursor(this.tail, null);
let acc = initialValue;
let item;
while (cursor.prev !== null) {
item = cursor.prev;
cursor.prev = item.prev;
acc = fn.call(thisArg, acc, item.data, item, this);
}
// pop cursor
this.releaseCursor();
return acc;
}
some(fn, thisArg = this) {
for (let cursor = this.head; cursor !== null; cursor = cursor.next) {
if (fn.call(thisArg, cursor.data, cursor, this)) {
return true;
}
}
return false;
}
map(fn, thisArg = this) {
const result = new List();
for (let cursor = this.head; cursor !== null; cursor = cursor.next) {
result.appendData(fn.call(thisArg, cursor.data, cursor, this));
}
return result;
}
filter(fn, thisArg = this) {
const result = new List();
for (let cursor = this.head; cursor !== null; cursor = cursor.next) {
if (fn.call(thisArg, cursor.data, cursor, this)) {
result.appendData(cursor.data);
}
}
return result;
}
nextUntil(start, fn, thisArg = this) {
if (start === null) {
return;
}
// push cursor
const cursor = this.allocateCursor(null, start);
while (cursor.next !== null) {
const item = cursor.next;
cursor.next = item.next;
if (fn.call(thisArg, item.data, item, this)) {
break;
}
}
// pop cursor
this.releaseCursor();
}
prevUntil(start, fn, thisArg = this) {
if (start === null) {
return;
}
// push cursor
const cursor = this.allocateCursor(start, null);
while (cursor.prev !== null) {
const item = cursor.prev;
cursor.prev = item.prev;
if (fn.call(thisArg, item.data, item, this)) {
break;
}
}
// pop cursor
this.releaseCursor();
}
// mutation
clear() {
this.head = null;
this.tail = null;
}
copy() {
const result = new List();
for (let data of this) {
result.appendData(data);
}
return result;
}
prepend(item) {
// head
// ^
// item
this.updateCursors(null, item, this.head, item);
// insert to the beginning of the list
if (this.head !== null) {
// new item <- first item
this.head.prev = item;
// new item -> first item
item.next = this.head;
} else {
// if list has no head, then it also has no tail
// in this case tail points to the new item
this.tail = item;
}
// head always points to new item
this.head = item;
return this;
}
prependData(data) {
return this.prepend(List.createItem(data));
}
append(item) {
return this.insert(item);
}
appendData(data) {
return this.insert(List.createItem(data));
}
insert(item, before = null) {
if (before !== null) {
// prev before
// ^
// item
this.updateCursors(before.prev, item, before, item);
if (before.prev === null) {
// insert to the beginning of list
if (this.head !== before) {
throw new Error('before doesn\'t belong to list');
}
// since head points to before therefore list doesn't empty
// no need to check tail
this.head = item;
before.prev = item;
item.next = before;
this.updateCursors(null, item);
} else {
// insert between two items
before.prev.next = item;
item.prev = before.prev;
before.prev = item;
item.next = before;
}
} else {
// tail
// ^
// item
this.updateCursors(this.tail, item, null, item);
// insert to the ending of the list
if (this.tail !== null) {
// last item -> new item
this.tail.next = item;
// last item <- new item
item.prev = this.tail;
} else {
// if list has no tail, then it also has no head
// in this case head points to new item
this.head = item;
}
// tail always points to new item
this.tail = item;
}
return this;
}
insertData(data, before) {
return this.insert(List.createItem(data), before);
}
remove(item) {
// item
// ^
// prev next
this.updateCursors(item, item.prev, item, item.next);
if (item.prev !== null) {
item.prev.next = item.next;
} else {
if (this.head !== item) {
throw new Error('item doesn\'t belong to list');
}
this.head = item.next;
}
if (item.next !== null) {
item.next.prev = item.prev;
} else {
if (this.tail !== item) {
throw new Error('item doesn\'t belong to list');
}
this.tail = item.prev;
}
item.prev = null;
item.next = null;
return item;
}
push(data) {
this.insert(List.createItem(data));
}
pop() {
return this.tail !== null ? this.remove(this.tail) : null;
}
unshift(data) {
this.prepend(List.createItem(data));
}
shift() {
return this.head !== null ? this.remove(this.head) : null;
}
prependList(list) {
return this.insertList(list, this.head);
}
appendList(list) {
return this.insertList(list);
}
insertList(list, before) {
// ignore empty lists
if (list.head === null) {
return this;
}
if (before !== undefined && before !== null) {
this.updateCursors(before.prev, list.tail, before, list.head);
// insert in the middle of dist list
if (before.prev !== null) {
// before.prev <-> list.head
before.prev.next = list.head;
list.head.prev = before.prev;
} else {
this.head = list.head;
}
before.prev = list.tail;
list.tail.next = before;
} else {
this.updateCursors(this.tail, list.tail, null, list.head);
// insert to end of the list
if (this.tail !== null) {
// if destination list has a tail, then it also has a head,
// but head doesn't change
// dest tail -> source head
this.tail.next = list.head;
// dest tail <- source head
list.head.prev = this.tail;
} else {
// if list has no a tail, then it also has no a head
// in this case points head to new item
this.head = list.head;
}
// tail always start point to new item
this.tail = list.tail;
}
list.head = null;
list.tail = null;
return this;
}
replace(oldItem, newItemOrList) {
if ('head' in newItemOrList) {
this.insertList(newItemOrList, oldItem);
} else {
this.insert(newItemOrList, oldItem);
}
this.remove(oldItem);
}
}
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