2.2 OddOccurrencesInArray

Solution

#include <set>int solution(vector<int> &A) { // write your code in C++11 (g++ 4.8.2) set<int> s; for (auto i: A) { if (s.find(i) == s.end()) { s.insert(i); } else { s.erase(i); } } return *s.begin();}