LeetCode 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 .
매번

class CharNode {

public:

    int count;

    CharNode* child[26];

    CharNode(int cnt = 0) : count(cnt) {

        for (int i = 0; i<26; i++) {

            child[i] = NULL;

        }

    }

};



class WordDictionary {

private:

    CharNode root;

    void add(const string& str) {

        CharNode* current = &root;

        int pos = 0;

        int len = str.size();

        char ch;

        while (pos < len) {

            ch = str[pos] - 'a';

            if (current->child[ch] == NULL) {

                current->child[ch] = new CharNode();

            }

            if (pos == len - 1) {

                current->child[ch]->count++;

            }

            current = current->child[ch];

            pos++;

        }

    }

    

    bool dfs_search(CharNode* at, string& word, int pos) {

        if (at == NULL) {

            return false;

        }

        int len = word.size();

        if (len == pos && at != NULL && at->count > 0) {

            return true;

        } else if (pos >= len) {

            return false;

        }

        if (word[pos] == '.') {

            // wildcard

            for (int i=0; i<26; i++) {

                if (dfs_search(at->child[i], word, pos + 1)) {

                    return true;

                }

            }

        } else {

            return dfs_search(at->child[word[pos] - 'a'], word, pos + 1);

        }

        return false;

    }

public:

    WordDictionary() {

        // placeholder for '\0' string

        root.count = 1;

    }

    // Adds a word into the data structure.

    void addWord(string word) {

        add(word);

    }



    // Returns if the word is in the data structure. A word could

    // contain the dot character '.' to represent any one letter.

    bool search(string word) {

        return dfs_search(&root, word, 0);

    }

};



// Your WordDictionary object will be instantiated and called as such:

// WordDictionary wordDictionary;

// wordDictionary.addWord("word");

// wordDictionary.search("pattern");