class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        counter = collections.Counter(nums)
        for key,value in counter.items():
            if value == 1: 
                return key

位运算 中等 每日一题 遍历检查就完事了

https://leetcode-cn.com/problems/single-number-ii/

或者也可以使用位运算的方法

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        a = b = 0
        for num in nums:
            a, b = (~a & b & num) | (a & ~b & ~num), ~a & (b ^ num)
        return b