题目

Design a data structure that supports the following two operations:

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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.

Example:

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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.

Python3:

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class WordDictionary:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        

    def addWord(self, word: str) -> None:
        """
        Adds a word into the data structure.
        """
        

    def search(self, word: str) -> bool:
        """
        Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
        """
        


# Your WordDictionary object will be instantiated and called as such:
# obj = WordDictionary()
# obj.addWord(word)
# param_2 = obj.search(word)

题解

题意:
完成WordDictionary类,addWord方法向词库中添加词,search方法用来搜索词,其中 ‘.’ 表示该位置可匹配任意字符. 所有单词只包含小写字母.

思路:
创建一颗树,在单词结尾节点进行标记以判断是否单词,遇到 ‘.’ 则对当前节点的所有子节点进行匹配.

代码:

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import collections as cl
class Node:
    def __init__(self):
        self.Children=cl.defaultdict(Node)
        self.isWord=False

class WordDictionary:

    def __init__(self):
        self.root=Node()
        """
        Initialize your data structure here.
        """

    def addWord(self, word: str) -> None:
        node = self.root
        for i in word:
            node =node.Children[i]
        node.isWord=True #对单词结尾标记
        """
        Adds a word into the data structure.
        """

    def search(self, word: str) -> bool:
        node = self.root
        self.res=False
        self.dfs(node,word)
        return self.res

        """
        Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
        """

    def dfs(self,node,word):
        if not word:
            if node.isWord:
                self.res = True
                return
            else :
                return
        if word[0]=='.':
            for j in node.Children.values():
                self.dfs(j,word[1:])
        else :
            node = node.Children.get(word[0])
            if not node:
                return
            self.dfs(node,word[1:])

# Your WordDictionary object will be instantiated and called as such:
# obj = WordDictionary()
# obj.addWord(word)
# param_2 = obj.search(word)