136. Single Number

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        dic = {}
        pop = dic.pop

        for i in nums:
            if i not in dic:
                dic[i] = None
            else:
                del (dic[i])

        return(dic.popitem()[0])
        
        
  class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        x = Counter(nums)
        for i in x:
            if x[i] == 1:
                return i


class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        stack = []
        for i in nums:
            if i not in stack:
                stack.append(i)
            else:
                stack.remove(i)
        return stack[0]
        

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        a = 0
        for i in nums:
            a ^= i
        return a