Add and Search Word - Data structure design

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.

click to show hint.

You should be familiar with how a Trie works. If not, please work on this problem: Implement Trie (Prefix Tree) first.

Solution

public class WordDictionary {

    TrieNode root;

    public class TrieNode {
        String val;
        Map<Character, TrieNode> map;

        public TrieNode() {
            map = new HashMap<>();
        }
    }


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

    // Adds a word into the data structure.
    public void addWord(String word) {
        if (word != null || word.length() >= 1) {
            addWord(word, 0, root);
        }
    }

    private void addWord(String word, int d, TrieNode current) {
        if (d == word.length()) {
            current.val = word;
            return;
        }

        char c = word.charAt(d);
        if (!current.map.containsKey(c)) {
            current.map.put(c, new TrieNode());
        }

        TrieNode node = current.map.get(c);
        addWord(word, d + 1, node);
    }

    // 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 false;
        }

        return search(word, 0, root);
    }


    private boolean search(String word, int d, TrieNode node) {
              if (d == word.length()) {
            if (node.val == null) {
                return false;
            }
            return true;
        }

        char c = word.charAt(d);
        if (c == '.') {

            for (TrieNode child : node.map.values()) {
                if (search(word, d + 1, child)) {
                    return true;
                }
            }

            return false;
        } else {
            if (node.map.containsKey(c)) {
                return search(word, d + 1, node.map.get(c));
            } else {
                return false;
            }
        }
    }
}

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