Sunday, September 28, 2025
HomeData Modelling & AIPython Set difference to find lost element from a duplicated array

Python Set difference to find lost element from a duplicated array

Given two arrays which are duplicates of each other except one element, that is one element from one of the array is missing, we need to find that missing element. Examples:

Input:  A = [1, 4, 5, 7, 9]
        B = [4, 5, 7, 9]
Output: [1]
1 is missing from second array.

Input: A = [2, 3, 4, 5
       B = 2, 3, 4, 5, 6]
Output: [6]
6 is missing from first array.

We have existing solution for this problem please refer Find lost element from a duplicated array. We can solve this problem quickly in python using Set difference logic. Approach is very simple, simply convert both lists in Set and perform A-B operation where len(A)>len(B). 

Implementation:

Python3




# Function to find lost element from a duplicate
# array
 
def lostElement(A,B):
     
    # convert lists into set
    A = set(A)
    B = set(B)
 
    # take difference of greater set with smaller
    if len(A) > len(B):
        print (list(A-B))
    else:
        print (list(B-A))
 
# Driver program
if __name__ == "__main__":
    A = [1, 4, 5, 7, 9]
    B = [4, 5, 7, 9]
    lostElement(A,B)


Output

[1]
Feeling lost in the world of random DSA topics, wasting time without progress? It’s time for a change! Join our DSA course, where we’ll guide you on an exciting journey to master DSA efficiently and on schedule.
Ready to dive in? Explore our Free Demo Content and join our DSA course, trusted by over 100,000 neveropen!

RELATED ARTICLES

Most Popular

Dominic
32324 POSTS0 COMMENTS
Milvus
84 POSTS0 COMMENTS
Nango Kala
6694 POSTS0 COMMENTS
Nicole Veronica
11859 POSTS0 COMMENTS
Nokonwaba Nkukhwana
11917 POSTS0 COMMENTS
Shaida Kate Naidoo
6807 POSTS0 COMMENTS
Ted Musemwa
7073 POSTS0 COMMENTS
Thapelo Manthata
6763 POSTS0 COMMENTS
Umr Jansen
6769 POSTS0 COMMENTS