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

巴特西

Leetcode 137. Single Number I/II/III

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