/
CircularSinglyLinkedList.ts
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CircularSinglyLinkedList.ts
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import { ForwardNode } from './Atomics';
import type { IForwardNode } from './types';
/**
* Implements a circular singly (linear) linked list.
*
* @public
*/
export class CircularSinglyLinkedList<T> {
/**
* The head node; implemented internally as a ring.
* The head is initialized to null; you must insert a node to initially populate the list.
*/
head: IForwardNode<T, CircularSinglyLinkedList<T>> | null;
/**
* The current size of the list
*
* @internal
*/
private length;
constructor() {
this.head = null;
this.length = 0;
}
/**
* Bootstrap a new head node
*/
private newHead(node: IForwardNode<T, CircularSinglyLinkedList<T>>) {
this.head = node;
node.next = this.head;
node.list = this;
this.length++;
return node;
}
/**
* Find the node prior to the given target
*/
private findNodeBefore(target: IForwardNode<T, CircularSinglyLinkedList<T>>) {
let tmp = this.head;
// we iterate until the `next` pointer points at the target
while (tmp && tmp.next != target) {
tmp = tmp.next;
}
if (!tmp) {
throw new Error(
'The list is malformed; there are no valid cases in which a node does not point to another'
);
}
return tmp;
}
/**
* Move given node *after* `at`, where `node` and `at` must be a member of the list
*
* @internal
*/
private move(
node: IForwardNode<T, CircularSinglyLinkedList<T>>,
at: IForwardNode<T, CircularSinglyLinkedList<T>>
) {
const tmp = this.findNodeBefore(node);
// it's a one-node list, so we return what is a head pointing to itself
if (tmp === node) {
return node;
}
// replace the node we're moving by connecting the nodes which sit astride it
tmp.next = node.next;
node.next = at.next;
at.next = node;
return node;
}
/**
* Instantiate an empty circular singly linked list
*/
static create() {
return new CircularSinglyLinkedList();
}
/**
* The current size of the list.
* This property does not account for a quasi-uninitialized head node.
*/
size() {
return this.length;
}
/**
* Returns the next list node, if extant; else, null
*
* @param node - A valid node, which must be a member of this list (return null if the given node is not a member).
* If this constraint is satisfied, return the next node from the given node.
*/
next(node: IForwardNode<T, CircularSinglyLinkedList<T>>) {
if (!node || !node.list || node.list !== this) {
return null;
}
return node.next;
}
/**
* Returns the previous list node, if extant; else, null
*
* @param node - A valid node, which must be a member of this list (return null if the given node is not a member).
* If this constraint is satisfied, return the previous node relative to the given node.
*/
prev(node: IForwardNode<T, CircularSinglyLinkedList<T>>) {
if (!node || !node.list || node.list !== this) {
return null;
}
return this.findNodeBefore(node);
}
/**
* Remove a given node from the list
*
* @param node - A node to remove from the list
*/
remove(node: IForwardNode<T, CircularSinglyLinkedList<T>>) {
if (!this.head || !node) {
return null;
}
if (node.list !== this) {
return null;
}
let tmp1: IForwardNode<T, CircularSinglyLinkedList<T>> = this.head;
let tmp2: IForwardNode<T, CircularSinglyLinkedList<T>>;
// starting with the head, cycle tmp1 until it matches the node to remove
while (tmp1 != node) {
if (!tmp1.next) {
throw new Error(
'The list is malformed; there are no valid cases in which a node does not point to another'
);
}
tmp2 = tmp1;
tmp1 = tmp1.next;
}
// if the node to remove is the head...
if (tmp1 === this.head) {
// cache the head
tmp2 = this.head;
// starting with the head, cycle tmp2 until its `next` points at the head
while (tmp2.next !== this.head) {
if (!tmp2.next) {
throw new Error(
'The list is malformed; there are no valid cases in which a node does not point to another'
);
}
tmp2 = tmp2.next;
}
// point our head at the old head's `next` (removing the original head)
this.head = this.head.next;
// repoint tmp2 at the new head
tmp2.next = this.head;
} else {
// tmp2 precedes tmp1, so we point its `next` at tmp1's `next` to remove tmp1
tmp2!.next = tmp1!.next; // we know these exist
}
node.list = null;
this.length--;
return node;
}
/**
* Excise the head of the list and return it; if the head is not extant, return null
*/
removeHead() {
if (!this.head) {
return null;
}
let tmp1: IForwardNode<T, CircularSinglyLinkedList<T>> = this.head;
const tmp2 = this.head;
// we've a single node list
if (tmp1.next === this.head) {
this.head = null;
} else {
// cycle until we've the node before head
while (tmp1.next !== this.head) {
if (!tmp1.next) {
throw new Error(
'The list is malformed; there are no valid cases in which a node does not point to another'
);
}
tmp1 = tmp1.next;
}
this.head = this.head.next;
tmp1.next = this.head;
}
this.length--;
tmp2.list = null;
return tmp2;
}
/**
* Remove the last node from the list
*/
pop() {
if (!this.head) {
return null;
}
let tmp = this.head;
while (tmp.next !== this.head) {
if (!tmp.next) {
throw new Error(
'The list is malformed; there are no valid cases in which a node does not point to another'
);
}
tmp = tmp.next;
}
return this.remove(tmp);
}
/**
* Move a given node to its new position after `mark`.
* If either the given node or mark are not an element of the list, or node == mark, the list is not modified.
* Both the node and mark must not be null.
*
* @param node - A node in the list to move
* @param mark - A node in the list after which to move `node`
*/
moveAfter(
node: IForwardNode<T, CircularSinglyLinkedList<T>>,
mark: IForwardNode<T, CircularSinglyLinkedList<T>>
) {
if (!node || !mark) {
return null;
}
if (node.list !== this || node === mark || mark.list !== this) {
return null;
}
if (mark.next === node) {
return null;
}
return this.move(node, mark);
}
/**
* Move a given node to its new position before `mark`.
* If either the given node or mark are not an element of the list, or node == mark, the list is not modified.
* Both the node and mark must not be null (return value will be null)
*
* @param node - A node in the list to move
* @param mark - A node in the list before which to move `node`
*/
moveBefore(
node: IForwardNode<T, CircularSinglyLinkedList<T>>,
mark: IForwardNode<T, CircularSinglyLinkedList<T>>
) {
if (!node || !mark) {
return null;
}
if (node.list !== this || node === mark || mark.list !== this) {
return null;
}
if (node.next === mark) {
return null;
}
const tmp = this.findNodeBefore(mark);
return this.move(node, tmp);
}
/**
* Push a new node with value `value` to the front of the list
*
* @param value - Push to the front of the list a node with the given value `value`
*/
pushFront(value: T) {
const node = ForwardNode<T, CircularSinglyLinkedList<T>>(value);
if (!this.head) {
return this.newHead(node);
}
const tmp = this.findNodeBefore(this.head);
node.next = this.head;
this.head = node;
tmp.next = this.head;
node.list = this;
this.length++;
return node;
}
/**
* Push a new node with value `value` to the back of the list
*
* @param value - Push to the back of the list a node with the given value `value`
*/
pushBack(value: T) {
const node = ForwardNode<T, CircularSinglyLinkedList<T>>(value);
if (!this.head) {
return this.newHead(node);
}
if (this.head && this.length == 1) {
this.head.next = node;
} else {
const tmp = this.findNodeBefore(this.head);
tmp.next = node;
}
node.next = this.head;
node.list = this;
this.length++;
return node;
}
/**
* Insert a new node with value `value` immediately after `mark`.
* If `mark` is not an element of the list, the list is not modified.
* `mark` must not be null.
*
* @param value - The value with which to instantiate the inserted node
* @param mark - A node in the list before which to insert the new node
*/
insertAfter(value: T, mark: IForwardNode<T, CircularSinglyLinkedList<T>>) {
// this list is circular, thus if a given node does not point to anything,
// we can presume its not a member of this list
if (!mark || !mark.next) {
return null;
}
if (mark.list !== this) {
return null;
}
const node = ForwardNode<T, CircularSinglyLinkedList<T>>(value);
if (!this.head) {
return this.newHead(node);
}
const tmp = this.findNodeBefore(mark.next);
if (tmp.next === this.head) {
tmp.next = node;
node.next = this.head;
} else {
node.next = tmp.next;
tmp.next = node;
}
node.list = this;
this.length++;
return node;
}
/**
* Insert a new node with value `value` immediately before `mark`.
* If `mark` is not an element of the list, the list is not modified.
* `mark` must not be null.
*
* @param value - The value with which to instantiate the inserted node
* @param mark - A node in the list before which to insert the new node
*/
insertBefore(value: T, mark?: IForwardNode<T, CircularSinglyLinkedList<T>>) {
if (!mark) {
return null;
}
if (mark.list !== this) {
return null;
}
const prev = this.prev(mark);
if (!prev) {
return null;
}
return this.insertAfter(value, prev);
}
/**
* Insert a copy of another list at the back of the caller list.
* The lists may be equivalent, but must not be null.
* @throws Throws if provided a list that is not an instance of `CircularDoublyLinkedList`
*/
pushBackList(other: this) {
if (!other || !other.head) {
return;
}
if (!(other instanceof CircularSinglyLinkedList)) {
throw new TypeError(
'`other` must be an instance of `CircularSinglyLinkedList`'
);
}
for (
let i = other.size(),
n: IForwardNode<T, CircularSinglyLinkedList<T>> | null = other.head;
i > 0;
i--, n = other.next(n)
) {
if (!n) {
throw new Error(
'`other` is malformed; there are no valid cases in which a node does not point to another'
);
}
this.pushBack(n.value as T);
}
}
/**
* Insert a copy of another list at the front of the caller list.
* The lists may be the same, but must not be null.
* @throws Throws if provided a list that is not an instance of `CircularDoublyLinkedList`
*/
pushFrontList(other: this) {
if (!other || !other.head) {
return;
}
if (!(other instanceof CircularSinglyLinkedList)) {
throw new TypeError(
'other must be an instance of `CircularSinglyLinkedList`'
);
}
for (
let i = other.size(), n = other.prev(other.head);
i > 0;
i--, n = other.prev(n)
) {
if (!n) {
throw new Error(
'`other` is malformed; there are no valid cases in which a node does not point to another'
);
}
this.pushFront(n.value as T);
}
}
}