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DoublyLinkedList.js
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DoublyLinkedList.js
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import DoublyLinkedListNode from './DoublyLinkedListNode';
import Comparator from '../../utils/comparator/Comparator';
export default class DoublyLinkedList {
/**
* @param {Function} [comparatorFunction]
*/
constructor(comparatorFunction) {
/** @var DoublyLinkedListNode */
this.head = null;
/** @var DoublyLinkedListNode */
this.tail = null;
this.compare = new Comparator(comparatorFunction);
}
/**
* @param {*} value
* @return {DoublyLinkedList}
*/
prepend(value) {
// Make new node to be a head.
const newNode = new DoublyLinkedListNode(value, this.head);
// If there is head, then it won't be head anymore.
// Therefore, make its previous reference to be new node (new head).
// Then mark the new node as head.
if (this.head) {
this.head.previous = newNode;
}
this.head = newNode;
// If there is no tail yet let's make new node a tail.
if (!this.tail) {
this.tail = newNode;
}
return this;
}
/**
* @param {*} value
* @return {DoublyLinkedList}
*/
append(value) {
const newNode = new DoublyLinkedListNode(value);
// If there is no head yet let's make new node a head.
if (!this.head) {
this.head = newNode;
this.tail = newNode;
return this;
}
// Attach new node to the end of linked list.
this.tail.next = newNode;
// Attach current tail to the new node's previous reference.
newNode.previous = this.tail;
// Set new node to be the tail of linked list.
this.tail = newNode;
return this;
}
/**
* @param {*} value
* @return {DoublyLinkedListNode}
*/
delete(value) {
if (!this.head) {
return null;
}
let deletedNode = null;
let currentNode = this.head;
while (currentNode) {
if (this.compare.equal(currentNode.value, value)) {
deletedNode = currentNode;
if (deletedNode === this.head) {
// If HEAD is going to be deleted...
// Set head to second node, which will become new head.
this.head = deletedNode.next;
// Set new head's previous to null.
if (this.head) {
this.head.previous = null;
}
// If all the nodes in list has same value that is passed as argument
// then all nodes will get deleted, therefore tail needs to be updated.
if (deletedNode === this.tail) {
this.tail = null;
}
} else if (deletedNode === this.tail) {
// If TAIL is going to be deleted...
// Set tail to second last node, which will become new tail.
this.tail = deletedNode.previous;
this.tail.next = null;
} else {
// If MIDDLE node is going to be deleted...
const previousNode = deletedNode.previous;
const nextNode = deletedNode.next;
previousNode.next = nextNode;
nextNode.previous = previousNode;
}
}
currentNode = currentNode.next;
}
return deletedNode;
}
/**
* @param {Object} findParams
* @param {*} findParams.value
* @param {function} [findParams.callback]
* @return {DoublyLinkedListNode}
*/
find({ value = undefined, callback = undefined }) {
if (!this.head) {
return null;
}
let currentNode = this.head;
while (currentNode) {
// If callback is specified then try to find node by callback.
if (callback && callback(currentNode.value)) {
return currentNode;
}
// If value is specified then try to compare by value..
if (value !== undefined && this.compare.equal(currentNode.value, value)) {
return currentNode;
}
currentNode = currentNode.next;
}
return null;
}
/**
* @return {DoublyLinkedListNode}
*/
deleteTail() {
if (!this.tail) {
// No tail to delete.
return null;
}
if (this.head === this.tail) {
// There is only one node in linked list.
const deletedTail = this.tail;
this.head = null;
this.tail = null;
return deletedTail;
}
// If there are many nodes in linked list...
const deletedTail = this.tail;
this.tail = this.tail.previous;
this.tail.next = null;
return deletedTail;
}
/**
* @return {DoublyLinkedListNode}
*/
deleteHead() {
if (!this.head) {
return null;
}
const deletedHead = this.head;
if (this.head.next) {
this.head = this.head.next;
this.head.previous = null;
} else {
this.head = null;
this.tail = null;
}
return deletedHead;
}
/**
* @return {DoublyLinkedListNode[]}
*/
toArray() {
const nodes = [];
let currentNode = this.head;
while (currentNode) {
nodes.push(currentNode);
currentNode = currentNode.next;
}
return nodes;
}
/**
* @param {*[]} values - Array of values that need to be converted to linked list.
* @return {DoublyLinkedList}
*/
fromArray(values) {
values.forEach(value => this.append(value));
return this;
}
/**
* @param {function} [callback]
* @return {string}
*/
toString(callback) {
return this.toArray().map(node => node.toString(callback)).toString();
}
/**
* Reverse a linked list.
* @returns {DoublyLinkedList}
*/
reverse() {
let currNode = this.head;
let prevNode = null;
let nextNode = null;
while (currNode) {
// Store next node.
nextNode = currNode.next;
// Change next node of the current node so it would link to previous node.
currNode.next = prevNode;
// Move prevNode and currNode nodes one step forward.
prevNode = currNode;
currNode = nextNode;
}
// Reset head and tail.
this.tail = this.head;
this.head = prevNode;
return this;
}
}