关键：

前缀树

 

class WordDictionary {
private:
    struct Trie{//建立前缀树
        Trie *children[26]{nullptr};
        bool is_string=false;
    };
    Trie *root;
public:
    /** Initialize your data structure here. */
    WordDictionary() {
        root=new Trie();
    }
    
    /** Adds a word into the data structure. */
    void addWord(string word) {
        Trie *note=root;
        for(const auto &w: word)
        {
            if(note->children[w-'a']==nullptr)note->children[w-'a']=new Trie();
            note=note->children[w-'a'];
        }
        note->is_string=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 dfs(root,word,0);
    }  
    
    bool dfs(Trie* root,string word,size_t i)
    {
        if(root==nullptr)return false;
        if(i>=word.size())return root->is_string;
        if(word[i]!='.')//该字符不为点.
        {
            if(root->children[word[i]-'a']!=nullptr)return dfs(root->children[word[i]-'a'],word,i+1);//该字符在前缀树中，继续深度优先搜索
            else return false;//该字符不再前缀树中，直接返回false
        }
        for(size_t j=0;j<26;++j)//遍历出root的后所有字符串路径，只要有一条字符串路径满足就返回true
        {
            if(root->children[j]&&dfs(root->children[j],word,i+1))return true;
        }
        return false;
    }
};