Symmetric Difference

Return elements that appear in exactly one of two collections.

sets set-operations symmetric-difference collections

Write a function `symmetric_difference(a, b)` that takes two lists `a` and `b` and returns a sorted list of elements that appear in exactly one of the two lists. Duplicate elements within each list should be treated as a single occurrence. The result must be sorted in ascending numeric order.

Constraints

The input lists can contain any integers. The lists may be empty or contain duplicates. The time complexity should be O(n log n) where n is the total number of unique elements.

Example

>>> symmetric_difference([1, 2, 3], [2, 3, 4])
[1, 4]
>>> symmetric_difference([1, 1, 2], [2, 3])
[1, 3]

8 points ~10 min

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Hints

Convert each list to a set to remove duplicates.

Use the set symmetric difference operator `^` or the method `.symmetric_difference()`.

Convert the result to a list and sort it before returning.

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