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.
You should be familiar with how a Trie works. If not, please work on this problem: Implement Trie (Prefix Tree) first.
LeetCode出新题的速度越来越快了，有点跟不上节奏的感觉了。这道题如果做过之前的那道Implement Trie (Prefix Tree) 实现字典树(前缀树)的话就没有太大的难度了，还是要用到字典树的结构，唯一不同的地方就是search的函数需要重新写一下，因为这道题里面'.'可以代替任意字符，所以一旦有了'.'，就需要查找所有的子树，只要有一个返回true，整个search函数就返回true，典型的DFS的问题，其他部分跟上一道实现字典树没有太大区别，代码如下：
class WordDictionary {
public:
struct TrieNode {
public:
TrieNode *child[];
bool isWord;
TrieNode() : isWord(false) {
for (auto &a : child) a = NULL;
}
};
WordDictionary() {
root = new TrieNode();
}
// Adds a word into the data structure.
void addWord(string word) {
TrieNode *p = root;
for (auto &a : word) {
int i = a - 'a';
if (!p->child[i]) p->child[i] = new TrieNode();
p = p->child[i];
}
p->isWord = 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) {
return searchWord(word, root, );
}
bool searchWord(string &word, TrieNode *p, int i) {
if (i == word.size()) return p->isWord;
if (word[i] == '.') {
for (auto &a : p->child) {
if (a && searchWord(word, a, i + )) return true;
}
return false;
} else {
return p->child[word[i] - 'a'] && searchWord(word, p->child[word[i] - 'a'], i + );
}
}
private:
TrieNode *root;
};
// Your WordDictionary object will be instantiated and called as such:
// WordDictionary wordDictionary;
// wordDictionary.addWord("word");
// wordDictionary.search("pattern");
讨论：这道题有个很好的Follow up，就是当搜索的单词中存在星号怎么搞，星号的定义和Wildcard Matching中一样，可以代表任意的字符串，包括空字符串，请参见评论区1楼。
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参考资料：
https://leetcode.com/discuss/36246/my-java-trie-based-solution