14. Implement_Trie.java

class TrieNode {

    // R links to node children
    private TrieNode[] links;

    private final int R = 26;

    private boolean isEnd;

    public TrieNode() {
        links = new TrieNode[R];
    }

    public boolean containsKey(char ch) {
        return links[ch -'a'] != null;
    }
    public TrieNode get(char ch) {
        return links[ch -'a'];
    }
    public void put(char ch, TrieNode node) {
        links[ch -'a'] = node;
    }
    public void setEnd() {
        isEnd = true;
    }
    public boolean isEnd() {
        return isEnd;
    }
}

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 node = root;
        for(int i=0;i<word.length();i++){
            char Curr = word.charAt(i);
            if(!node.containsKey(Curr)){
                node.put(Curr, new TrieNode());
            }
            node= node.get(Curr);
        }
        node.setEnd();
    }
    
    
    private TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
           char curLetter = word.charAt(i);
           if (node.containsKey(curLetter)) {
               node = node.get(curLetter);
           } else {
               return null;
           }
        }
        return node;
    }
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
       return node != null && node.isEnd();
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode node = searchPrefix(prefix);
        return node != null;
    }
}

/**
 * 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);
 */