Trie.java

/**
 * 208. Implement Trie (Prefix Tree)
 *
 * Implement a trie with insert, search, and startsWith methods.
 *
 * Note:
 * You may assume that all inputs are consist of lowercase letters a-z.
 */

/**
 * For Recursive version of the Trie implementation, see
 * https://github.com/fluency03/leetcode-java/blob/master/src/ImplementTriePrefixTree208.java
 */

public 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 c = word.charAt(i);
            if (!node.containsKey(c)) {
                node.put(c, new TrieNode());
            }
            node = node.get(c);
        }
        node.setLeaf();
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if (!node.containsKey(c)) {
                return false;
            }
            node = node.get(c);
        }
        return node.isLeaf();
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode node = root;
        for (int i = 0; i < prefix.length(); i++) {
            char c = prefix.charAt(i);
            if (!node.containsKey(c)) {
                return false;
            }
            node = node.get(c);
        }
        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);
 */