ImplementTrie.java

/*
 * Implement a trie with insert, search, and startsWith methods.

 Notice

You may assume that all inputs are consist of lowercase letters a-z.

Example
insert("lintcode")
search("code") // return false
startsWith("lint") // return true
startsWith("linterror") // return false
insert("linterror")
search("lintcode) // return true
startsWith("linterror") // return true
 */
public class ImplementTrie {

    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode cur = root;
        for (char c : word.toCharArray()) {
            if (cur.children[c - 'a'] == null) {
                cur.children[c - 'a'] = new TrieNode();
            }
            cur = cur.children[c - 'a'];
        }
        cur.item = word;
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode cur = root;
        for (char c : word.toCharArray()) {
            if (cur.children[c - 'a'] == null) {
                return false;
            }
            cur = cur.children[c - 'a'];
        }
        return cur.item.equals(word);
    }

    // Returns if there is any word in the trie 
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode cur = root;
        for (char c : prefix.toCharArray()) {
            if (cur.children[c - 'a'] == null) {
                return false;
            }
            cur = cur.children[c - 'a'];
        }
        return true;
    }

}

class TrieNode {

    TrieNode[] children;
    String item;

    // Initialize your data structure here.
    public TrieNode() {
        children = new TrieNode[26];
        item = "";
    }

}