Что не нравится валидатору?
package com.javarush.task.task18.task1803;
/*
Самые частые байты
*/
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
FileInputStream inputStream = new FileInputStream(reader.readLine());
int[] buffer = new int[inputStream.available()];
if (inputStream.available() > 0) {
while (inputStream.available() > 0) {
for(int i = 0; i < buffer.length; i++) {
buffer[i] = inputStream.read();
}
}
}
HashSet<Integer> duplicates = new HashSet<>();
for (int i = 0; i < buffer.length; i++)
{
if (duplicates.contains(buffer[i]))
{
continue;
}
for (int j = i + 1; j < buffer.length; j++)
{
if (buffer[i] == (buffer[j]))
{
duplicates.add(buffer[i]);
break;
}
}
}
System.out.println(duplicates);
inputStream.close();
}
}