131 lines
3.1 KiB
JavaScript
131 lines
3.1 KiB
JavaScript
const head = Symbol("head");
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const tail = Symbol("tail");
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class CircularDoublyLinkedListNode {
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constructor (data) {
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this.data = data;
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this.next = null;
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this.previous = null;
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}
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}
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export class CircularDoublyLinkedList {
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constructor () {
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this[head] = null;
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this[tail] = null;
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}
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add (data) {
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const newNode = new CircularDoublyLinkedListNode(data);
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// Special case: no items in the list
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if (this[head] === null) {
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this[head] = newNode;
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newNode.next = newNode;
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newNode.previous = newNode;
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} else {
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const tail = this[head].previous;
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tail.next = newNode;
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newNode.previous = tail;
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newNode.next = this[head];
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this[head].previous = newNode;
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}
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}
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get (index) {
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if ( ! Number(index) < 0) {
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return undefined;
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}
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let current = this[head];
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let i = 0;
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do {
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if (i === index) {
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return current.data;
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}
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current = current.next;
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i++;
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} while ((current !== this[head]) && (i <= index));
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return undefined;
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}
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remove (index) {
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if ((this[head] === null) || (index < 0)) {
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throw new RangeError(`Index ${index} does not exist in the list.`);
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}
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let current = this[head];
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// Removing the first node
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if (index === 0) {
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if (current.next === this[head]) {
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this[head] = null;
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} else {
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const tail = this[head].previous;
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// Set the tail to point to the second item in the list
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// and point the new item to the tail
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tail.next = current.next;
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current.next.previous = tail;
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this[head] = tail.next;
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}
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return current.data;
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}
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let i = 0;
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do {
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current = current.next;
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i++;
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} while ((current !== this[head]) && (i < index));
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if (current !== this[head]) {
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// skip over the node to remove it
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current.previous.next = current.next;
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current.next.previous = current.previous;
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return current.data;
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}
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throw new RangeError(`Index ${index} does not exist in the list.`);
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}
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*values () {
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// list is empty
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if (this[head] !== null) {
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// only one node
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if (this[head].next === this[head]) {
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yield this[head].data;
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} else {
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let current = this[head];
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do {
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yield current.data;
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current = current.next;
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} while (current !== this[head]);
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}
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}
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}
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*circularValues () {
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if (this[head] !== null) {
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let current = this[head];
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// infinite loop
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while (true) {
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yield current.data;
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current = current.next;
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}
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}
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}
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[Symbol.iterator] () {
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return this.values();
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}
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} |