[LeetCode] Implement Trie (Prefix Tree).java

class TrieNode {
    // Initialize your data structure here.
    private Map<Character, TrieNode> children;
    private boolean isWord;

    public TrieNode() {
        this.children = new HashMap<>();
    }
    
    TrieNode addLetter(Character letter) {
        if (!children.containsKey(letter)) {
            children.put(letter, new TrieNode());
        }
        return children.get(letter);
    }
    
    TrieNode getChild(Character letter) {
        return children.get(letter);
    }
    
    void setIsWord() {
        isWord = true;
    }
    
    boolean isWord() {
        return isWord;
    }
}

public class Trie {
    private TrieNode root;

    public Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode currentNode = root;
        for (int i = 0; i < word.length(); i++) {
            currentNode = currentNode.addLetter(word.charAt(i));
        }
        currentNode.setIsWord();
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode currentNode = root;
        for (int i = 0; i < word.length(); i++) {
            currentNode = currentNode.getChild(word.charAt(i));
            if (currentNode == null) {
                return false;
            }
        }
        return currentNode.isWord();
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode currentNode = root;
        for (int i = 0; i < prefix.length(); i++) {
            currentNode = currentNode.getChild(prefix.charAt(i));
            if (currentNode == null) {
                return false;
            }
        }
        return true;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");