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interface Skiplist {    search: (target: number) => boolean;    add: (num: number) => void;    erase: (num: number) => boolean;}
function Skiplist(): Skiplist {    const storage = new Map<number, number>();
    function search(target: number): boolean {        return storage.has(target) && (storage.get(target) || 0) > 0;    }
    function add(num: number): void {        storage.set(num, 1 + (storage.get(num) || 0));    }
    function erase(num: number): boolean {        if (storage.get(num) === 1) {            storage.delete(num);
            return true;        }        if (search(num)) {            storage.set(num, -1 + (storage.get(num) || 0));            return true;        } else {            return false;        }    }    return { search, add, erase };}
export default Skiplist;