Given an array of integers, every element appearsthreetimes except for one, which appears exactly once. Find that single one.

**Note:** Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

题目连接

https://leetcode.com/problems/single-number-ii/description/

需要实现一个3次计数,

class Solution:# @param {integer[]} nums# @return {integer}def singleNumber(self, nums):x, y = 0, 0for num in nums:x = (x ^ num) & (~y)y = (y ^ num) & (~x)return x