Где ошибка? В "хотелке" валидатора сделать через TreeMap?
public class Solution {
public static void main(String[] args) throws Exception {
try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
try (FileInputStream stream = new FileInputStream(reader.readLine())) {
ArrayList<Integer> bytesList = new ArrayList<>();
while (stream.available() > 0) {
if (!bytesList.contains(stream.read())) {
bytesList.add(stream.read());
}
}
Collections.sort(bytesList);
for (Integer b : bytesList) {
System.out.print(b + " ");
}
}
}
}
}