import java.util.LinkedHashMap;
import java.util.Map;

public class Solution {
    public static Integer oddOccurrencesInArray(int[] a) {
        Map<Integer, Integer> count = new LinkedHashMap<>();

        for (int value : a) {
            if (!count.containsKey(value)) {
                count.put(value, 1);
            } else {
                count.remove(value);
            }
        }

        for (Integer key : count.keySet()) {
            return key;
        }

        return null;
    }
}