211.Design Add and Search Words Data Structure
===

###### tags: `Medium`,`String`,`DFS`,`Trie`

[211. Design Add and Search Words Data Structure](https://leetcode.com/problems/design-add-and-search-words-data-structure/)

### 題目描述

Design a data structure that supports adding new words and finding if a string matches any previously added string.

Implement the `WordDictionary` class:

* `WordDictionary()` Initializes the object.
* `void addWord(word)` Adds `word` to the data structure, it can be matched later.
* `bool search(word)` Returns `true` if there is any string in the data structure that matches `word` or `false` otherwise. `word` may contain dots `'.'` where dots can be matched with any letter.

### 範例

**Example 1:**

Input
["WordDictionary","addWord","addWord","addWord","search","search","search","search"]
[[],["bad"],["dad"],["mad"],["pad"],["bad"],[".ad"],["b.."]]
Output
[null,null,null,null,false,true,true,true]

Explanation
WordDictionary wordDictionary = new WordDictionary();
wordDictionary.addWord("bad");
wordDictionary.addWord("dad");
wordDictionary.addWord("mad");
wordDictionary.search("pad"); // return False
wordDictionary.search("bad"); // return True
wordDictionary.search(".ad"); // return True
wordDictionary.search("b.."); // return True

**Constraints**:

* 1 <= `word.length` <= 25
* `word` in `addWord` consists of lowercase English letters.
* `word` in `search` consist of `'.'` or lowercase English letters.
* There will be at most 3 dots in `word` for `search` queries.
* At most 10^4^ calls will be made to `addWord` and `search`.

### 解答

### Reference

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