Leetcode 211. Add and Search Word - Data structure design

最新推荐文章于 2019-08-05 10:40:12 发布

原创最新推荐文章于 2019-08-05 10:40:12 发布 · 372 阅读

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#Trie

本文介绍了一种使用Trie数据结构实现单词字典的方法，支持两种操作：添加单词(addWord)和根据正则表达式进行搜索(search)，其中正则表达式可以包含任意字母或'.'符号，'.'可以匹配任何一个字母。

Problem

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

Solution

用 Trie实现就好了。

但是有一点很容易出错，什么时候才能算是找到？first thought是走到叶子节点才行，其实不然，比如

add "ab" , add "a" , 然后 search "a", 这样因为还没有到达叶子节点b 就返回错；

修正：

每个TreeNode都加一个属性是否是单词的最后一个字符（isLast）

struct TreeNode2 {
    TreeNode2(char c) : letter(c), isLast(false) {}
    char letter;
    vector<TreeNode2*> neighbs;
    bool isLast;
};

class WordDictionary {
    TreeNode2* root;
    void addHelper(TreeNode2* root, int idx, const string& word){
        if(idx == word.size()){
            return;
        }
        for( auto neighb : root->neighbs) {
            if( word[idx] == neighb->letter){
                return addHelper( neighb, idx + 1, word);
            }
        }
        TreeNode2* newNeighb = new TreeNode2(word[idx]);
        if( idx == word.size() -1) { newNeighb->isLast = true;}
        (root->neighbs).push_back(newNeighb);
        return addHelper( newNeighb, idx+1, word);
        
    }
    bool searchHelper(TreeNode2* root, int idx, const string& word){
        if(idx == word.size() && root->isLast) return true;
        if(idx == word.size()) return false;
        
        if( word[idx] == '.' ){
             for( auto neighb : root->neighbs ) {
                 if( searchHelper( neighb, idx + 1, word)) return true;
             }
        }
        
        
        for( auto neighb : root->neighbs ){
            if( neighb->letter == word[idx]) {
                return searchHelper( neighb, idx + 1, word);
            }
        }
        return false;
    }
public:
    WordDictionary():root(new TreeNode2('0')){}
    
    // Adds a word into the data structure.
    void addWord(string word) {
        addHelper(root, 0, word);
    }

    // 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 searchHelper( root, 0, word);
    }
};

// Your WordDictionary object will be instantiated and called as such:
// WordDictionary wordDictionary;
// wordDictionary.addWord("word");
// wordDictionary.search("pattern");