[Lesson 2] Arrays - OddOccurrencesInArray

https://app.codility.com/programmers/lessons/2-arrays/odd_occurrences_in_array/

OddOccurrencesInArray coding task - Learn to Code - Codility

import java.util.HashSet;
import java.util.Set;
import java.util.stream.Collectors;

class Solution {
    public int solution(int[] A) {
        Set<Integer> numSet = new HashSet<>();

        for (int num : A) {
            if (numSet.contains(num)) {
                numSet.remove(num);
            } else {
                numSet.add(num);
            }
        }

        return numSet.stream().collect(Collectors.toList()).get(0);
    }
}