Add and Search Word - Data structure design - LeetCode

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.

思路：构建字典树。搜索时，若当前字符为'.'，则将字典中当前位置存在的字符都搜索一遍。

 class DictNode
 {
 public:
     DictNode *dict[];
     DictNode ()
     {
         for (int i = ; i < ; i++)
             dict[i] = NULL;
     }
 };
 class WordDictionary {
 public:
     WordDictionary()
     {
         root = new DictNode();
     }
     // Adds a word into the data structure.
     void addWord(string word) {
         DictNode *cur = root;
         for (int i = , len = word.size(); i < len; i++)
         {
             int loc = (int)(word[i] - 'a');
             if (cur->dict[loc] == NULL)
                 cur->dict[loc] = new DictNode();
             cur = cur->dict[loc];
         }
         if (cur->dict[] == NULL)
             cur->dict[] = new DictNode();
     }
     bool help(DictNode *cur, string word)
     {
         if (cur == NULL) return false;
         if (word.size() == )
         {
             if (cur->dict[] == NULL) return false;
             return true;
         }
         if (word[] != '.')
         {
             int loc = (int)(word[] - 'a');
             return help(cur->dict[loc], (word.size() >  ? word.substr() : ""));
         }
         else
         {
             for (int i = ; i < ; i++) if (cur->dict[i] != NULL)
             {
                 if (help(cur->dict[i], (word.size() >  ? word.substr() : "")))
                     return true;
             }
             return false;
         }
     }

     // 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 help(root, word);
     }
 private:
     DictNode *root;
 };

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