import java.util.*; class Main { public static void main(String[] args) { List<Integer> a = new ArrayList<>(Arrays.asList(1,2,3,4,3,2,1)); int length = a.size(); HashMap<Integer, Integer> lonely = new HashMap<>(); for (int i = 0; i < length; i++) { int count = 0; for (int j = 0; j < length; j++) { if(a.get(i) == a.get(j)){ count++; lonely.put(a.get(i), count); } } } System.out.println(lonely); } }