int firstDuplicate(std::vector<int> a) {
    struct duplicate
    {
        int positionOfDuplicate = NULL;
        int duplicateValue = NULL;
    };

    duplicate duplactedNumber;

    for(int numberChecking = 0 ; numberChecking<a.size() && (numberChecking < duplactedNumber.positionOfDuplicate ||
    duplactedNumber.positionOfDuplicate == NULL) ; numberChecking++)
    {
        for(int potentialDuplicate = numberChecking + 1 ; (potentialDuplicate<duplactedNumber.positionOfDuplicate ||
        duplactedNumber.positionOfDuplicate == NULL)
        && potentialDuplicate < a.size() ; potentialDuplicate++)
        {
            if(a.at(numberChecking) == a.at(potentialDuplicate)
            && (numberChecking < duplactedNumber.positionOfDuplicate || duplactedNumber.positionOfDuplicate == NULL))
            {
                duplactedNumber.positionOfDuplicate = potentialDuplicate;
                duplactedNumber.duplicateValue = a.at(potentialDuplicate);
                break;
            }
        }
    }

    if(duplactedNumber.duplicateValue == NULL)
    {
        return -1;
    }
    else
    {
        return duplactedNumber.duplicateValue;
    }
}