Google's Foo.bar Two Array Difference Puzzle (Prison Labor Dodgers)

gfc_l1q1_solution.py

# Quiz: Prison Labor Dodgers
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# Commander Lambda is all about efficiency, including using her bunny prisoners for manual labor. But no one's been properly monitoring the labor shifts for a while, and they've gotten quite mixed up. You've been given the task of fixing them, but after you wrote up new shifts, you realized that some prisoners had been transferred to a different block and aren't available for their assigned shifts. And manually sorting through each shift list to compare against prisoner block lists will take forever - remember, Commander Lambda loves efficiency!

# Given two almost identical lists of prisoner IDs x and y where one of the lists contains an additional ID, write a function answer(x, y) that compares the lists and returns the additional ID.

# For example, given the lists x = [13, 5, 6, 2, 5] and y = [5, 2, 5, 13], the function answer(x, y) would return 6 because the list x contains the integer 6 and the list y doesn't. Given the lists x = [14, 27, 1, 4, 2, 50, 3, 1] and y = [2, 4, -4, 3, 1, 1, 14, 27, 50], the function answer(x, y) would return -4 because the list y contains the integer -4 and the list x doesn't.

# In each test case, the lists x and y will always contain n non-unique integers where n is at least 1 but never more than 99, and one of the lists will contain an additional unique integer which should be returned by the function.  The same n non-unique integers will be present on both lists, but they might appear in a different order, like in the examples above. Commander Lambda likes to keep her numbers short, so every prisoner ID will be between -1000 and 1000.

# Solution
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def answer(x, y):
    return list(set(x).symmetric_difference(set(y)))[0]