com.javarush.task.task36.task3605

Solution.java

package com.javarush.task.task36.task3605;

import java.util.*;
import java.nio.file.*;
import java.io.*;

/* 
Использование TreeSet
*/
public class Solution {
    public static void main(String[] args) throws IOException {
        Files.lines(Paths.get(args[0]))
            .map(String::toLowerCase)
            .flatMapToInt(String::chars)
            .distinct()
            .filter(Character::isAlphabetic)
            .sorted()
            .limit(5)
            .mapToObj(x -> (char)x)
            .forEach(System.out::print);
        System.out.println();
    }
}