Trie

public class SimpleTrie {

    public class TrieNode {
        boolean valid;
        TrieNode[] children;
    }

    public TrieNode root;

    private TrieNode getNode() {
        TrieNode t = new TrieNode();
        t.valid = false;
        t.children = new TrieNode[26];
        return t;
    }

    public SimpleTrie() {
        root = getNode();
    }

    public void insert(String key) {
        TrieNode crawler = root;
        for(int level=0 ; level < key.length() ; level++) {
            int index = key.charAt(level) - 'A';
            if(crawler.children[index] == null) {
                crawler.children[index] = getNode();
            }
            crawler = crawler.children[index];
        }
        crawler.valid = true;
    }

    public boolean contains(String key) {
        TrieNode crawler = root;
        for(int level=0 ; level < key.length() ; level++) {
            int index = key.charAt(level) - 'A';
            if(crawler.children[index] == null) {
                return false;
            }
            crawler = crawler.children[index];
        }
        return (crawler != null) && (crawler.valid == true);
    }
}