Given an array a that contains only numbers in the range from 1 to a.length, find the first duplicate number for which the second occurrence has the minimal index. In other words, if there are more than 1 duplicated numbers, return the number for which the second occurrence has a smaller index than the second occurrence of the other number does.…

firstDublicate

def firstDuplicate(a):
    """ This function return a first doublicate element if it exit and return -1 if it does not ."""
    new_set = set()
    for i in a:
       if i in new_set:
           return i
       else:   
           new_set.add(i)
            
    if len(new_set)== len(a):         
        return -1