Implement a trie with insert, search, and startsWith methods.
Note:
You may assume that all inputs are consist of lowercase letters a-z.

總結Trie：http://www.reibang.com/p/357c1dbe31ec

Solution1：Trie

思路： Basic Trie
Time Complexity: O(word_num * word_len)
Space Complexity: O(number of nodes)

Solution1 Code：

class TrieNode {
    public TrieNode[] children = new TrieNode[26];
    public boolean isWord;
}

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

    public void insert(String word) {
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(cur.children[c - 'a'] == null){
                cur.children[c - 'a'] = new TrieNode();
            }
            cur = cur.children[c - 'a'];
        }
        cur.isWord = true;
    }

    public boolean search(String word) {
        TrieNode cur = root; 
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(cur.children[c - 'a'] == null) return false;
            cur = cur.children[c - 'a'];
        }
        return cur.isWord;
    }

    public boolean startsWith(String prefix) {
        TrieNode cur = root; 
        for(int i = 0; i < prefix.length(); i++){
            char c = prefix.charAt(i);
            if(cur.children[c - 'a'] == null) return false;
            cur = cur.children[c - 'a'];
        }
        return true;
    }
}

Solution1.Round1 Code：

class Trie {
    
    class TrieNode {
        public TrieNode[] children = new TrieNode[26];;
        public boolean is_word;
        public char val;

        public TrieNode(char c) {
            this.val = c;
        }
    }


    private TrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode('0');
    }
    
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if(cur.children[c - 'a'] == null) {
                cur.children[c - 'a'] = new TrieNode(c);
            }
            cur = cur.children[c - 'a'];
        }
        cur.is_word = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if(cur.children[c - 'a'] == null) {
                return false;
            }
            cur = cur.children[c - 'a'];
        }
        return cur.is_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(int i = 0; i < prefix.length(); i++) {
            char c = prefix.charAt(i);
            if(cur.children[c - 'a'] == null) {
                return false;
            }
            cur = cur.children[c - 'a'];
        }
        return true;
    }
}