剑指 Offer 56 - II. 数组中数字出现的次数 II

思路：建立哈希表

Python：

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        adict={}
        for i in range(len(nums)):
            if nums[i] not in adict:
                adict[nums[i]]=1
            else:
                adict[nums[i]]+=1
        for key in adict:
            if adict[key]==1:
                return key