Given an array of integers, every element appears twice except for one. Find that single one.

本题利用XOR的特性， X^0 = X, X^X = 0, 并且XOR满足交换律。

 

1 class Solution(object): 2     def singleNumber(self, nums): 3         """ 4         :type nums: List[int] 5         :rtype: int 6         """ 7         s = 0 8         for x in nums: 9             s= s^x10         11         return s

 

single number II/III可以用位操作。用Hash table也可以通过OJ

class Solution(object):    def singleNumber(self, nums):        """        :type nums: List[int]        :rtype: int        """        dict = {}        for i in range(len(nums)):            if nums[i] not in dict:                dict[nums[i]] = 1            else:                dict[nums[i]] += 1                for word in dict:            if dict[word] == 1:                return word