leetcode.211. Add and Search Word - Data structure design字典树

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.

用到字典树

 class TrieNode  
   {  
public:  
    bool isEnd;  
    TrieNode *children[26];  
    TrieNode() : isEnd(false)  
    {  
        for (int i = 0; i < 26; i++)  
        {  
            children[i] = NULL;  
        }  
    }  
}; 
class WordDictionary {
public:
    WordDictionary()  
    {  
        root = new TrieNode();  
    }  
      

    // Adds a word into the data structure.
    void addWord(string word) {
        TrieNode *cur = root;  
        for (int i = 0; i < word.length(); i++)  
        {  
            int index = word[i] - 'a';  
            if (cur->children[index] == NULL)  
            {  
                cur->children[index] = new TrieNode();  
            }  
  
            cur = cur->children[index];  
        }  
  
        cur->isEnd = true;   
    }

    // 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) {
        int n = word.length();  
        return search(word, n, 0, root); 
    }
    bool search(string &word, int n, int pos, TrieNode *cur)  
    {  
        if (cur == NULL)  
        {  
            return false;  
        }  
        if (pos == n)  
        {  
            return cur->isEnd;  
        }  
  
        if (word[pos] == '.')  
        {  
            for (int i = 0; i < 26; i++)  
            {  
                if (cur->children[i])  
                {  
                    if (search(word, n, pos+1, cur->children[i]))  
                    {  
                        return true;  
                    }  
                }  
            }  
        }  
        else  
        {  
            int index = word[pos] - 'a';  
            if (cur->children[index])  
            {  
                return search(word, n, pos+1, cur->children[index]);  
            }  
        }  
  
        return false;  
    }  
private:  
    TrieNode *root;  
};