Solution.java

class Trie {

    class TrieNode {

        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;
        }
    }

    private TrieNode root;

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

    public void insert(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char currentChar = word.charAt(i);
            if (!node.containsKey(currentChar)) {
                node.put(currentChar, new TrieNode());
            }
            node = node.get(currentChar);
        }
        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;
    }

    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
        return node != null && node.isEnd();
    }

    public boolean startsWith(String prefix) {
        TrieNode node = searchPrefix(prefix);
        return node != null;
    }
}