python find the duplicate number code example

Example 1: python find first duplicate numbers

def findDuplicateNumbers(a):
  mySet = set()
    for el in a:
        if el in mySet:
            return el
        mySet.add(el)
    return -1

Example 2: python check for duplicate

def checkDuplicate(user):
    if len(set(user)) < len(user):
        return True
    return False