ImplementTrie.java

class TrieNode {
    // Initialize your data structure here.
    public TrieNode[] list;
    public boolean leaf;
    public TrieNode() {
        list = new TrieNode[26];
        leaf = false;
    }
}

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode current = root;
        for (int i = 0; i < word.length(); i++) {
            int index = word.charAt(i) - 'a';
            if (current.list[index] == null) {
                current.list[index] = new TrieNode();
            }
            current = current.list[index];
        }
        current.leaf = true;
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode current = root;
        for (int i = 0; i < word.length(); i++) {
            int index = word.charAt(i) - 'a';
            if (current.list[index] == null) return false;
            else current = current.list[index];
        }
        return current.leaf;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode current = root;
        for (int i = 0; i < prefix.length(); i++) {
            int index = prefix.charAt(i) - 'a';
            if (current.list[index] == null) return false;
            else current = current.list[index];
        }
        return true;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");