LC 0136 [E] Single Number

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        # O(n), O(n)
        freqs = Counter(nums)
        
        for num, freq in freqs.items():
            if freq == 1:
                return num
            
    def singleNumber(self, nums: List[int]) -> int:
        # O(n), O(1)
        a = 0
        for i in nums:
            a ^= i
        return a