208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

class TrieNode{
    public TrieNode[] children;
    public boolean isEnd;
    public TrieNode(){
        children = new TrieNode[26];
    }
}

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