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export interface NumberIterator {    hasNext(): boolean;    next(): number;}interface PeekingIterator {    peek(): number | null;
    next(): number | null;
    hasNext(): boolean;}export default PeekingIterator;function PeekingIterator(iterator: NumberIterator): PeekingIterator {    let nextElement: null | number = iterator.next();    function peek(): number | null {        return nextElement;    }
    function next(): number | null {        const ret = nextElement;        nextElement = iterator.hasNext() ? iterator.next() : null;        return ret;    }
    function hasNext(): boolean {        return nextElement != null;    }    return { peek, next, hasNext };}