function lonelyinteger(a: number[]): number {
    if (a.length === 1) return a[0];
    
    const arrMap = new Map<number, number>();
    
    a.forEach((n:number) => (arrMap.has(n)) ? arrMap.set(n, (arrMap.get(n) + 1)) : arrMap.set(n, 1));
    const iterator = arrMap.entries();
    
    for (let i = 0; i < arrMap.size; i++){
        const results = iterator.next().value;
        if (results[1] === 1) return results[0]
    }
}