208. Implement Trie (Prefix Tree)

class TrieNode {
    Boolean isWord;
    TrieNode[] children;
    public TrieNode(){
        this.isWord = false;
        this.children = new TrieNode[26];
    }
}
class Trie {
    TrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode current = root;
        for(int i=0;i<word.length();i++){
            int index = (int)word.charAt(i)-'a';
            if(current.children[index] == null)
                current.children[index] = new TrieNode();
            current = current.children[index];
        }
        current.isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode current = root;
        for(int i=0;i<word.length();i++){
            int index = (int)word.charAt(i)-'a';
            if(current.children[index]==null)
                return false;
            current = current.children[index];
        }
        return current.isWord;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
         TrieNode current = root;
        for(int i=0;i<prefix.length();i++){
            int index = (int)prefix.charAt(i)-'a';
            if(current.children[index]==null)
                return false;
            current = current.children[index];
        }
        return true;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */