leetcode211

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211. Add and Search Word - Data structure design

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.

Example:

addWord(“bad”)
addWord(“dad”)
addWord(“mad”)
search(“pad”) -> false
search(“bad”) -> true
search(“.ad”) -> true
search(“b..”) -> true

Idea

Trie (for add) + Dfs (for search)

Code

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class TrieNode():
    def __init__(self):
        self.children = {}
        self.isWord = False

class WordDictionary(object):
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.root = TrieNode()
        
    def addWord(self, word):
        """
        Adds a word into the data structure.
        :type word: str
        :rtype: void
        """
        node = self.root
        for c in word:
            if c not in node.children:
                node.children[c] = TrieNode()
            node = node.children[c]
        node.isWord = True

    def search(self, word):
        """
        Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
        :type word: str
        :rtype: bool
        """
        self.ans = False
        self.dfs(0, word, self.root)
        return self.ans

    def dfs(self, pos, word, root):
        if pos >= len(word):
            if root.isWord:
                self.ans = True
            return
        
        if word[pos] == '.':
            for c in root.children:
                self.dfs(pos+1, word, root.children[c])
        else:
            if word[pos] in root.children:
                self.dfs(pos+1, word, root.children[word[pos]])