leetcode 137

137. Single Number II

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

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

数组仅有一个数出现一次，其他的出现3次。找出那个出现一次的数。依然使用位运算来求解。

统计每一位上1出现的次数，1出现次数不为3的倍数的位所组成的数即为要找的数。

代码实现：

 class Solution {
 public:
     int singleNumber(vector<int>& nums) {
         int n = nums.size();
         int ones = ;
         int twos = ;
         int xthrees = ;
         for(int i = ; i < n; ++i)
         {
             twos |= (ones & nums[i]);
             ones ^= nums[i];
             xthrees = ~(ones & twos);
             ones &= xthrees;
             twos &= xthrees;
         }
         return ones;
     }
 };