211. Add and Search Word - Data structure design

https://leetcode.com/problems/add-and-search-word-data-structure-design/

public class WordDictionary {
    
    private TrieNode root = new TrieNode();
    
    private static class TrieNode { 
        // declared static since don't need to refer any member of parent class
        boolean isEndOfWord;
        TrieNode[] children;
        public TrieNode() {
            isEndOfWord = false;
            children = new TrieNode[26];
        }
    }

    // Adds a word into the data structure.
    public void addWord(String word) {
        TrieNode cur = root;
        for (char c : word.toCharArray()) {
            if (cur.children[c - 'a'] == null) {
                cur.children[c - 'a'] = new TrieNode();
            }
            cur = cur.children[c - 'a'];
        }    
        cur.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 search (word, root);
    }
    
    public boolean search(String word, TrieNode root) {
        // search for word start from cur TrieNode
        TrieNode cur = root;
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if (c == '.') { // skip current node
                for (TrieNode child : cur.children) {
                    // try every child of the children of current node
                    // if any of them is true, then return true
                    if (child != null) {
                        if (search(word.substring(i + 1), child)) {
                            return true;
                        }
                    }
                }
                return false;
            } else {
                if (cur.children[c - 'a'] == null) {
                    return false;
                }
                cur = cur.children[c - 'a'];
            }
        }
        return cur.isEndOfWord;
    }
}

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