208. Implement Trie (Prefix Tree)

class Trie {

    Trie[] children=new Trie[26];
    
    boolean isWord=false;
    
    /** Initialize your data structure here. */
    public Trie() {
        
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        if(word.length()==0)
        {
            isWord=true;
            return;
        }
        int idx=word.charAt(0)-'a';
        if(children[idx]==null)
            children[idx]=new Trie();
        children[idx].insert(word.substring(1));
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        if(word.length()==0)
            return isWord;
        int idx=word.charAt(0)-'a';
        if(children[idx]!=null)
            return children[idx].search(word.substring(1));
        return false;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        if(prefix.length()==0)
            return true;
        int idx=prefix.charAt(0)-'a';
        if(children[idx]!=null)
            return children[idx].startsWith(prefix.substring(1));
        return false;
    }
}