duplicates

import java.util.HashSet;
import java.util.Set;

public class Main {

    public static void main(String[] args) {
        int[] age = {1,2,5,10,29,19,20,19,2,1,50,10,2,5,100,100,16,61,13,16,5,10};

        Set<Integer> foundUniques = new HashSet<>();
        Set<Integer> duplicates = new HashSet<>();

        for (int i = 0; i < age.length; i++) {
            foundUniques.add(age[i]);
            if(i+1 >= age.length) break;

            if(foundUniques.contains(age[i+1])) duplicates.add(age[i+1]);
        }

        for (Integer i:
             duplicates) {
            System.out.println(i);
        }
    }
}