Dictionary.java

import java.util.HashMap;
import java.util.Map;

public class Dictionary implements IDictionary {

    private Node root = new Node();

    private static class Node {
        Map<Character, Node> children = new HashMap<>();
        Node parent = null;
        String value = null;
    }

    @Override
    public boolean put(String key, String value) {
        try {
            Node currentNode = root;
            Node currentParent;

            for(char character : key.toCharArray()) {
                if (!currentNode.children.containsKey(character)) {
                    currentNode.children.put(character, new Node());
                }

                currentParent = currentNode;
                currentNode = currentNode.children.get(character);

                currentNode.parent = currentParent;
            }

            currentNode.value = value;

            return true;

        } catch (Exception e) {
            System.out.println("Добавление не удалось. Причина: " + e.getMessage());
            return false;
        }
    }

    @Override
    public String get(String key) {
        Node currentNode = root;

        for (char character : key.toCharArray()) {
            if (!currentNode.children.containsKey(character)) {
                return null;
            } else {
                currentNode = currentNode.children.get(character);
            }
        }

        return currentNode.value;
    }

    @Override
    public boolean remove(String key) {
        try {

            Node currentNode = root;

            for (char character : key.toCharArray()) {
                if (!currentNode.children.containsKey(character)) {
                    return false;
                } else {
                    currentNode = currentNode.children.get(character);
                }
            }

            currentNode.value = null;

            while (currentNode.parent != null && currentNode.children.size() == 0) {
                Node currentParent = currentNode.parent;
                if (currentParent.children.size() == 1 && currentNode.value == null) {
                    currentParent.children.clear();
                    currentNode = currentParent;
                }
                else {
                    break;
                }
            }

            return true;

        } catch (Exception e) {
            System.out.println("Удаление не удалось. Причина: " + e.getMessage());
            return false;
        }
    }

    @Override
    public boolean isEmpty() {
        return root.children.isEmpty();
    }
}