Leetcode 448. Find All Numbers Disappeared in an Array

# Runtime: 364 ms, faster than 82.09% of Python3 online submissions for Find All Numbers Disappeared in an Array.
# Memory Usage: 23.8 MB, less than 7.14% of Python3 online submissions for Find All Numbers Disappeared in an Array.

class Solution:
    def findDisappearedNumbers(self, nums: List[int]) -> List[int]:
        _set = set()
        ans = []

        for num in nums:
            _set.add(num)

        for num in range(1, len(nums) + 1):
            if num not in _set:
                ans.append(num)

        return ans

https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/