Find Missing Numbers in an Array

Hi, here's your problem today. This problem was recently asked by Twitter:

Given an array of integers of size n, where all elements are between 1 and n inclusive, find all of the elements of [1, n] that do not appear in the array. Some numbers may appear more than once.

Example:
Input: [4,5,2,6,8,2,1,5]
Output: [3,7]

class Solution(object):

  def findDisappearedNumbers(self, nums):

    # Fill this in.



nums = [4, 6, 2, 6, 7, 2, 1]

print(Solution().findDisappearedNumbers(nums))

# [3, 5]

For this problem, you can assume that you can mutate the input array.