/* Codility - OddOccurrenceslnArray */

// you can use includes, for example:

#include <iostream>

#include <map>

#include <vector>

using namespace std;

// you can write to stdout for debugging purposes, e.g.

// cout << "this is a debug message" << endl;

int solution(vector<int> &A) {

// write your code in C++14 (g++ 6.2.0)

int len = A.size();

map<int, int> m; // key, 갯수

vector<bool> check(1000000001);

for(int i=0;i<len;i++) {

// 없으면

// if(m.find(A[i]) == m.end()) {

if(check[A[i]] == false) {

m.insert(make_pair(A[i], 1));

check[A[i]] = true;

} else {

m[A[i]]++;

}

}

// map 돌면서 갯수가 홀수인 애 찾아서 리턴

len = m.size();

for(auto iter=m.begin(); iter != m.end(); iter++) {

if((iter->second)%2 == 1){

return iter->first;

}

}

}

int main(){

int arr[5] = {2, 2, 3, 3, 4};

vector<int> test;

for(int i=0;i<5;i++) {

test.push_back(arr[i]);

}

printf("%d\n",solution(test));

}