Leetcode 137. Single Number I/II/III

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。

 class Solution(object):
     def singleNumber(self, nums):
         """
         :type nums: List[int]
         :rtype: int
         """
         s = 0
         for x in nums:
             s= s^x

         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