[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.

字典树，注意匹配 '.' 的时候要对所有的子树进行匹配，这时就得用DFS了。

 1 class WordDictionary {

 2 private:

 3     struct trinode {

 4         trinode *ch[26];

 5         bool iskey;

 6         trinode(): iskey(false) {

 7             for (auto &a : ch) a = NULL;

 8         }

 9     };

10     

11     trinode *root;

12     

13     void _addWord(string s) {

14         trinode *p = root;

15         for (auto &a : s) {

16             int idx = a - 'a';

17             if (p->ch[idx] == NULL) p->ch[idx] = new trinode();

18             p = p->ch[idx];

19         }

20         p->iskey = true;

21     }

22     

23     bool _search(trinode *root, string s, int pos) {

24         if (pos == s.length()) return root->iskey;

25         if (s[pos] == '.') {

26             for (auto &p : root->ch) {

27                 if (p != NULL && _search(p, s, pos + 1)) return true;

28             }

29             return false;

30         } else {

31             int idx = s[pos] - 'a';

32             return (root->ch[idx] && _search(root->ch[idx], s, pos + 1));

33         }

34     }

35     

36 public:

37     WordDictionary() {

38         root = new trinode();

39     }

40     // Adds a word into the data structure.

41     void addWord(string word) {

42         _addWord(word);

43     }

44 

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

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

47     bool search(string word) {

48         return _search(root, word, 0);

49     }

50 };

51 

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

53 // WordDictionary wordDictionary;

54 // wordDictionary.addWord("word");

55 // wordDictionary.search("pattern");

 搜索的时候可以只有遇到 '.' 的时候才递归，否则就迭代。可以提高一点点效率。

 1     bool _search(trinode *root, string s, int pos) {

 2         if (pos == s.length()) return root->iskey;

 3         trinode *p = root;

 4         for (; pos < s.length(); ++pos) {

 5             if (s[pos] != '.') {

 6                 int idx = s[pos] - 'a';

 7                 if (p->ch[idx] == NULL) return false;

 8                 p = p->ch[idx];

 9             } else {

10                 for (int idx = 0; idx < 26; ++idx) {

11                     if (p->ch[idx] && __search(p->ch[idx], s, pos + 1)) return true;

12                 }

13                 return false;

14             }

15         }

16         return p->iskey;

17     }