AddAndSearchWord.java

public class AddAndSearchWord {
 /**
 Design a data structure that supports the following two operations:

 void addWord(word)
 bool search(word)
 search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.

 Example:

 addWord("bad")
 addWord("dad")
 addWord("mad")
 search("pad") -> false
 search("bad") -> true
 search(".ad") -> true
 search("b..") -> true
 Note:
 You may assume that all words are consist of lowercase letters a-z.
 */
 class Node {
 boolean isWord;
 char val;
 Node[] children;
 public Node(char val, boolean isWord) {
 this.val = val;
 children = new Node[26];
 this.isWord = isWord;
 }
 }

 private Node head; // Store a dummy node that have 26 children
 /** Initialize your data structure here. */
 public AddAndSearchWord() {
 head = new Node('A', false);
 }

 /** Adds a word into the data structure. */
 public void addWord(String word) {
 if (word == null) return;
 char[] cArr = word.toCharArray();
 Node cur = head;
 for (char c : cArr) {
 if (cur.children[c - 'a'] == null) {
 cur.children[c - 'a'] = new Node(c, false);
 }
 cur = cur.children[c - 'a'];
 }
 cur.isWord = true;
 }

 /** Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter. */
 public boolean search(String word) {
 if (word == null || word.length() == 0) return true;
 return search(word, this.head);
 }

 /**
 Return true if there is word under the given head
 */
 public boolean search(String word, Node head) {
 if (word == null || head == null) return false;
 if (word.length() == 0 && head.isWord) return true;
 if (word.length() == 0) return false;
 char c = word.charAt(0);
 if (c == '.') {
 for (Node child : head.children) {
 if (search(word.substring(1, word.length()), child))
 return true;
 }
 return false;
 }
 return search(word.substring(1, word.length()), head.children[c - 'a']);
 }

/**
 * Your WordDictionary object will be instantiated and called as such:
 * WordDictionary obj = new WordDictionary();
 * obj.addWord(word);
 * boolean param_2 = obj.search(word);
 */
}