AddAndSearchWordDataStructureDesign.java

// 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.

// For 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.

public class AddAndSearchWordDataStructure {
    public class TrieNode {
        public TrieNode[] children = new TrieNode[26];
        public String item = "";
    }
    
    private TrieNode root = new TrieNode();

    public void addWord(String word) {
        TrieNode node = root;

        for (char c : word.toCharArray()) {
            if (node.children[c - 'a'] == null) {
                node.children[c - 'a'] = new TrieNode();
            }

            node = node.children[c - 'a'];
        }

        node.item = word;
    }

    public boolean search(String word) {
        return match(word.toCharArray(), 0, root);
    }
    
    private boolean match(char[] chs, int k, TrieNode node) {
        if (k == chs.length) {
            return !node.item.equals(""); 
        }

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

        return false;
    }
}