53 lines
1.3 KiB
TypeScript
53 lines
1.3 KiB
TypeScript
export interface List<T> extends Iterable<T> {
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item: T | null;
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next: List<T> | null;
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toArray(): Array<T>;
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}
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export function atEnd<T>(xs: List<T>): xs is (List<T> & { item: null, next: null }) {
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return xs.item === null;
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}
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export function notAtEnd<T>(xs: List<T>): xs is (List<T> & { item: T, next: List<T> }) {
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return xs.item !== null;
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}
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export class ArrayList<T> implements List<T> {
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readonly items: Array<T>;
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readonly index: number = 0;
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constructor(items: Array<T>, index = 0) {
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this.items = items;
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this.index = index;
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}
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get item(): T | null {
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return this.items[this.index] ?? null;
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}
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get next(): List<T> | null {
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if (this.index >= this.items.length) return null;
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return new ArrayList(this.items, this.index + 1);
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}
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toArray(): Array<T> {
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return this.items.slice(this.index);
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}
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[Symbol.iterator](): Iterator<T> {
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let i: List<T> = this;
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return {
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next(): IteratorResult<T> {
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if (notAtEnd(i)) {
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const value = i.item;
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i = i.next;
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return { done: false, value };
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} else {
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return { done: true, value: null };
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}
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}
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};
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}
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}
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