645. Set Mismatch

https://leetcode.com/problems/set-mismatch/

Python

class Solution:
    def findErrorNums(self, nums: List[int]) -> List[int]:
        full_nums = set([n for n in range(1, len(nums)+1)])
        
        missed = full_nums - set(nums)
        
        seen = set()
        for num in nums:
            if num not in seen:
                seen.add(num)
                continue
            return [num, missed.pop()]