OddOccurrencesInArray

#include <algorithm>

int solution(vector<int> &A) {
    // write your code in C++11 (g++ 4.8.2)
    std::sort(A.begin(), A.end());
    if(A.size() <= 2 || A[0] != A[1])
        return A.front();
    for(auto it = A.begin() + 2; it < A.end()-2; it += 2)
    {
        if(*it != *(it+1))
        {
            if(*(it+1) != *(it+2))
                return *++it;
            return *it;
        }
    }
    return A.back();
}