Прошу проверить ДЗ4

src/ru/gb/Dmitrieva/HomeWorkApp/Lesson_4/Main.java

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+package ru.gb.Dmitrieva.HomeWorkApp.Lesson_4;
+
+import java.util.*;
+
+public class Main {
+    public static void main(String[] args) {
+
+        System.out.println("\n###Задание 1###");
+
+        String[] words = new String[]{
+                "команда", "банк", "сцена", "население", "свобода",
+                "музыка", "правда", "свобода", "память", "команда",
+                "память", "свобода", "договор", "дерево", "банк",
+                "свобода", "музыка", "большинство", "сцена", "музыка"
+        };
+        List<String> wordsList = Arrays.asList(words);
+        System.out.println("Все слова: " + wordsList);
+
+        Set<String> wordsSet = new HashSet<>(wordsList);
+        System.out.println("Уникальные слова: " + wordsSet);
+
+        for (String word : wordsSet) {
+            int number = Collections.frequency(wordsList, word);
+            System.out.println(word + " : " + number);
+        }
+
+        System.out.println("\n###Задание 2###");
+
+        Phonebook phonebook = new Phonebook();
+        System.out.println("-Добавляем Иванова.");
+        phonebook.add("Иванов", "+79261425312");
+        System.out.println("1) Иванов - " + phonebook.get("Иванов"));
+        System.out.println("1) Сидоров - " + phonebook.get("Сидоров"));
+
+        System.out.println("\n-Добавляем Сидорова.");
+        phonebook.add("Сидоров", "+79157437375");
+        System.out.println("2) Иванов - " + phonebook.get("Иванов"));
+        System.out.println("2) Сидоров - " + phonebook.get("Сидоров"));
+
+        System.out.println("\n-Добавляем второго Иванова.");
+        phonebook.add("Иванов", "+79062431890");
+        System.out.println("3) Иванов - " + phonebook.get("Иванов"));
+        System.out.println("3) Сидоров - " + phonebook.get("Сидоров"));
+    }
+}

src/ru/gb/Dmitrieva/HomeWorkApp/Lesson_4/Phonebook.java

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+package ru.gb.Dmitrieva.HomeWorkApp.Lesson_4;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class Phonebook {
+    private HashMap<String, HashSet<String>> phonebook;
+
+    public Phonebook() {
+        this.phonebook = new HashMap<>();
+    }
+
+    public HashSet<String> get(String surname) {
+        if (phonebook.containsKey(surname))
+            return phonebook.get(surname);
+        return new HashSet<>(Collections.singletonList(""));
+    }
+
+    public boolean add(String surname, String phone) {
+        if (phonebook.containsKey(surname)) {
+            HashSet<String> numberSet = phonebook.get(surname);
+            if (!numberSet.contains(phone)) {
+                numberSet.add(phone);
+            } else {
+                return false;
+            }
+        } else {
+            HashSet<String> numberSet = new HashSet<>(1);
+            numberSet.add(phone);
+            phonebook.put(surname, numberSet);
+        }
+        return true;
+    }
+}