duplicate.py

def containsDuplicate(nums):
    num_set = set()
    for num in nums:
        if num in num_set:
            return True
        num_set.add(num)
    return False

nums1 = [1,2,3,1]
print(containsDuplicate(nums1)); # True

nums2 = [1,2,3,4]
print(containsDuplicate(nums2));  # False

nums3 = [1,1,1,3,3,4,3,2,4,2]
print(containsDuplicate(nums3))   # True