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]; } } };