第九周：137. Single Number II

Given an array of integers, every element appears three times 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?

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AC：

class Solution {public:    int singleNumber(vector<int>& nums) {          int n = nums.size();        sort(nums.begin(), nums.end());        if(nums[0] != nums[1])            return nums[0];        if(nums[n-1] != nums[n-2])            return nums[n-1];        for(int i = 1; i < n-1; i ++)        {            if(nums[i] != nums[i-1] && nums[i] != nums[i+1])                return nums[i];        }    }};