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doubly-linked-list.ts
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doubly-linked-list.ts
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class Node {
data: any;
prev: Node;
next: Node = null;
constructor(data: any, prev: Node) {
this.data = data;
this.prev = prev;
}
}
/**
* A doubly-linked list data structure, where each node in the list contains
* references for both the node before it and the node after it.
*/
export default class DoublyLinkedList {
head: Node = null;
tail: Node = null;
/** Adds an element to the tail end of the list. */
add(element: any): void {
if (this.tail) {
this.tail.next = new Node(element, this.tail);
this.tail = this.tail.next;
} else {
this.head = new Node(element, null);
this.tail = this.head;
}
}
/**
* Removes all occurrences of the given element from the list (or returns
* `null` if the element is not present).
*/
remove(element: any): void | null {
if (this.head) {
// Removes as many heads as necessary
while (this.head.data === element) {
this.head = this.head.next;
this.head.prev = null;
}
// Removes as many tails as necessary
while (this.tail.data === element) {
this.tail = this.tail.prev;
this.tail.next = null;
}
// Iterate through rest of list
let currentNode = this.head.next;
while (currentNode.next) {
if (currentNode.data === element) {
// Link adjacent nodes
currentNode.prev.next = currentNode.next;
currentNode.next.prev = currentNode.prev;
}
currentNode = currentNode.next;
}
} else {
return null;
}
}
/** Clears the contents of the list. */
clear(): void {
this.head = null;
this.tail = null;
}
/** Reverses the list in place (or returns `null` if the list is empty). */
reverse(): void | null {
if (this.head) {
this.head = this.tail;
let currentNode = this.head;
while (currentNode.prev) {
// Swap adjacent nodes
const oldPrev = currentNode.prev;
currentNode.prev = currentNode.next;
currentNode.next = oldPrev;
currentNode = currentNode.next;
}
// Set new tail
this.tail = currentNode;
this.tail.prev = this.tail.next;
this.tail.next = null;
} else {
return null;
}
}
}