How to Check if Array/List Contains Duplicate Numbers or Strings in Python using Set?

python

In Python, we can check if an array or list contains duplicate items using the following one-liner function.

def contain_duplicates(list):
    return len(set(list)) != len(list)

The idea is to convert the list/array to set, then we can use the len function to get the sizes of the set and the original list/array. If they are both equal, then the array or list does not contain any duplicate items.

>>> contain_duplicates([1,2,3,4])
False
>>> contain_duplicates([1,2,3,4,2])
True
>>> contain_duplicates(["aa", "bb"])
False
>>> contain_duplicates(["aa", "bb", "aa"])
True

Alternatively, you can use the following naive solution based on set.

def contain_duplicates(list):
   data = set()
   for i in list:
      if i in data:
         return True
      data.add(i)
   return False 

The time complexity is O(N) and the space requirement is O(N) as well given the size of the list is N.

–EOF (The Ultimate Computing & Technology Blog) —