Add and Search Word - Data structure design

Source

• leetcode: Add and Search Word

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")  // return false
search("bad")  // return true
search(".ad")  // return true
search("b..")  // return true
Note
You may assume that all words are consist of lowercase letters a-z.

Java

class TrieNode{
    TrieNode[] children;
    boolean isEndOfWord;

    public TrieNode() {
        this.isEndOfWord = false;
        this.children = new TrieNode[26];
    }
}

public class WordDictionary {
    private TrieNode root;

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

    // Adds a word into the data structure.
    public void addWord(String word) {
        TrieNode runner = root;
        for(char c : word.toCharArray()){
            if(runner.children[c-'a']==null){
                runner.children[c-'a'] = new TrieNode();
            }
            runner = runner.children[c-'a'];
        }
        runner.isEndOfWord = 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) {
        return match(word.toCharArray(), 0, root);
    }

    public boolean match(char[] word, int k, TrieNode node) {
        if (k == word.length) return node.isEndOfWord;
        if (word[k] != '.') {
            return node.children[word[k] - 'a'] != null && match(word, k+1, node.children[word[k] - 'a']);
        }
        else {
            for (int i = 0; i < node.children.length; i++) {
                if (node.children[i] != null) {
                    if (match(word, k+1, node.children[i])) return true;
                }
            }
        }
        return false;
    }
}

// Your WordDictionary object will be instantiated and called as such:
// WordDictionary wordDictionary = new WordDictionary();
// wordDictionary.addWord("word");
// wordDictionary.search("pattern");