Trie树

Trie树：字典查找树。

208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

Solution

class TrieNode(object):
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.word = False
        self.children = {}

class Trie(object):

    def __init__(self):
        self.root = TrieNode()

    def insert(self, word):
        """
        Inserts a word into the trie.
        :type word: str
        :rtype: void
        """
        node = self.root
        for i in word:
            if i not in node.children:
                node.children[i] = TrieNode()
            node = node.children[i]
        node.word = True

    def search(self, word):
        """
        Returns if the word is in the trie.
        :type word: str
        :rtype: bool
        """
        node = self.root
        for i in word:
            if i not in node.children:
                return False
            node = node.children[i]
        return node.word

    def startsWith(self, prefix):
        """
        Returns if there is any word in the trie
        that starts with the given prefix.
        :type prefix: str
        :rtype: bool
        """
        node = self.root
        for i in prefix:
            if i not in node.children:
                return False
            node = node.children[i]
        return True

# Your Trie object will be instantiated and called as such:
# trie = Trie()
# trie.insert("somestring")
# trie.search("key")

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.

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.

Solution

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

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 i in word:
            if i not in node.children:
                node.children[i] = TrieNode()
            node = node.children[i]
        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
        """
        return self.helper(word, self.root)
        
    def helper(self, word, node):
        if len(word) == 0:
            return node.isWord
        first = word[0]
        if first == ".":
            for key in node.children:
                # return true if any was true
                if self.helper(word[1:], node.children[key]):
                    return True
        else:
            if first not in node.children:
                return False
            return self.helper(word[1:], node.children[first])
        return False
            
        

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