Day-22-Single Number II.cpp

Given a non-empty 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?

Example 1:

Input: [2,2,3,2]
Output: 3
Example 2:

Input: [0,1,0,1,0,1,99]
Output: 99









class Solution {
public:
    int singleNumber(vector<int>& nums) {
        unordered_map<int, int> m;
        for(auto x: nums)
            m[x]++;
        for(auto it=m.begin(); it!=m.end(); it++)
            if(it->second==1) return it->first;
        return -1; // result not found
    }
};