Given two sets of data A and B, each containing a sequence of values, how would you compute the difference between them?

To compute the difference between two sets of data A and B, you can treat them as sets and use the set difference operation. In Python, you can convert the lists to sets and compute A - B. For example:

A = [1, 1, 1, 2, 2, 3, None, None]

B = [1, 2, 3, None]

# Convert to sets to remove duplicates

set_a = set(A)

set_b = set(B)

# Difference

difference = set_a - set_b

print(difference) # Output: {None}

If you need to preserve duplicates, you can use collections.Counter to count occurrences and subtract counts. In SQL, you can use the EXCEPT clause or a LEFT JOIN with a NULL check:

SELECT value FROM A

EXCEPT

SELECT value FROM B;

The complexity of set conversion and difference is O(n) where n is the total number of elements. Handling NULLs depends on the language: in Python, None is a valid element; in SQL, NULL is not equal to NULL, so you may need to handle it explicitly. The key idea is to treat the data as collections and apply the appropriate difference operation.