Find the missing element between two arrays in Python

The challenge

Given two integer arrays where the second array is a shuffled duplicate of the first array with one element missing, find the missing element.

Please note, there may be duplicates in the arrays, so checking if a numerical value exists in one and not the other is not a valid solution.

find_missing([1, 2, 2, 3], [1, 2, 3]) => 2
Code language: PHP (php)
find_missing([6, 1, 3, 6, 8, 2], [3, 6, 6, 1, 2]) => 8
Code language: PHP (php)

The first array will always have at least one element.

Test cases

Test.it("Basic tests") Test.assert_equals(find_missing([1, 2, 3], [1, 3]), 2) Test.assert_equals(find_missing([6, 1, 3, 6, 8, 2], [3, 6, 6, 1, 2]), 8) Test.assert_equals(find_missing([7], []), 7) Test.assert_equals(find_missing([4, 3, 3, 61, 8, 8], [8, 61, 8, 3, 4]), 3) Test.assert_equals(find_missing([0, 0, 0, 0, 0], [0, 0, 0, 0]), 0)
Code language: Python (python)

The solution in Python

Option 1 (using sum):

def find_missing(arr1, arr2): return sum(arr1)-sum(arr2)
Code language: Python (python)

Option 2 (using reduce):

from functools import reduce from operator import xor def find_missing(xs, ys): return reduce(xor, xs, 0) ^ reduce(xor, ys, 0)
Code language: Python (python)

Option 3 (removing from list):

def find_missing(a, b): for x in b: a.remove(x) return a[0]
Code language: Python (python)
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