import java.util.*;
import java.util.stream.Collectors;

public class WordsForLetter {

    public static void main(String[] args) {
        String input = "ala ma, kota";
        Map<Character, List<String>> resullt = new HashMap<>();
        List<Character> keys = getKeys(input);
        String[] splitedInput = splitInputIntoWords(input);
        createWordsListForKey(resullt, keys, splitedInput);
        printResult(resullt);
    }

    private static void printResult(Map<Character, List<String>> result) {
        result.forEach((key, value) -> System.out.println(
                key + ":" + value));
    }

    private static void createWordsListForKey(Map<Character, List<String>> result, List<Character> keys, String[] s) {
        for (Character key : keys) {
            List<String> words = new ArrayList<>();
            for (String str : s) {
                if (str.indexOf(key) != -1) {
                    result.get(key).add(str);
                }
            }
            result.put(key, words);
        }
    }

    private static String[] splitInputIntoWords(String input) {
        return input.split(" ");
    }

    private static List<Character> getKeys(String input) {
        return input.chars()
                .filter(Character::isLetter)
                .distinct()
                .mapToObj(intToChar -> (char) intToChar)
                .collect(Collectors.toList());
    }

}