文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

Single Number II

2. Solution

• Simple Method

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        int i = 0;
        while(i < nums.size() - 1) {
            if(nums[i] == nums[i + 1]) {
                i += 3;
            }
            else {
                return nums[i];
            }
        }
        return nums[nums.size() - 1];
    }
};

• O(N)

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int a = 0;
        int b = 0;
        for(int i = 0; i < nums.size(); i++) {
            a = (a ^ nums[i]) & (~b);
            b = (b ^ nums[i]) & (~a);
        }
        return a;
    }
};

Reference

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

2. https://leetcode.com/problems/single-number-ii/discuss/43294/Challenge-me-thx