MapNode

package example.test.google;

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

public class TFK {

    public static void main(String[] args) {

        TFK test = new TFK();
        test.test();
    }

    public void test() {
        String sentence = "this is a test";
        Path path = Path.sentenceToPath(sentence);

        Node root = new Node();

        NodeOperate.addNode(root, path);

        sentence = "this is another test";
        path = Path.sentenceToPath(sentence);
        NodeOperate.addNode(root, path);
    }
}

class Node {
    String key;
    Node value;
    Map<String, Node> pair;
}

class NodeOperate {

    public static void addNode(Node node, Path path) {

        if (node == null || path == null) {
            return;
        }

        if (contains(node, path)) {

            Node next = findNode(node, path);
            if (next != null) {
                updateNode(node);
                addNode(next, path.next);
            }
        } else {
            Node next = new Node();

            saveNode(node, path, next);

            addNode(next, path.next);
        }
    }

    public static void addNode0(Node node, Path path) {

        if (node == null || path == null) {
            return;
        }

        if (contains(node, path)) {
            Node next = findNode(node, path);
            addNode(next, path.next);
        } else {
            Node next = new Node();

            if (node.key != null) {
                updateNode(node);
            }
            saveNode(node, path, next);

            addNode(next, path.next);
        }
    }

    public static Node findNode(Node node, Path path) {
        if (node.key != null) {
            if (node.key.equals(path.word)) {
                return node.value;
            }
        }

        return node.pair.get(path.word);
    }

    public static void saveNode(Node node, Path path, Node next) {
        if (node.pair != null) {
            node.pair.put(path.word, next);
        } else {
            node.key = path.word;
            node.value = next;
        }
    }

    public static void updateNode(Node node) {
        if (node.pair == null) {
            node.pair = new HashMap<>();
        }

        node.pair.put(node.key, node.value);

        node.key = null;
        node.value = null;
    }

    public static boolean contains(Node node, Path path) {

        if (node.pair != null) {
            return node.pair.containsKey(path.word);
        }

        if (node.key != null) {
            return node.key.equals(path.word);
        }
        return false;
    }
}