[leetcode] 208. Implement Trie (Prefix Tree) @ python

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原题

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

Example:

Trie trie = new Trie();

trie.insert(“apple”);
trie.search(“apple”); // returns true
trie.search(“app”); // returns false
trie.startsWith(“app”); // returns true
trie.insert(“app”);
trie.search(“app”); // returns true
Note:

You may assume that all inputs are consist of lowercase letters a-z.
All inputs are guaranteed to be non-empty strings.

解法

参考:
花花酱 LeetCode 208. Implement Trie (Prefix Tree)
AC Python Solution
定义TrieNode类, 它的孩子是字典, 字典的key是字母, value是TrieNode. 每个TrieNode的属性包含是否为单词.

代码

class TrieNode(object):
    def __init__(self):
        self.children = collections.defaultdict(TrieNode)
        self.is_word = False
        
class Trie(object):

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

    def insert(self, word):
        """
        Inserts a word into the trie.
        :type word: str
        :rtype: void
        """
        curr = self.root
        for ch in word:
            curr = curr.children[ch]
        curr.is_word = True            

    def search(self, word):
        """
        Returns if the word is in the trie.
        :type word: str
        :rtype: bool
        """
        curr = self.root
        for ch in word:
            curr = curr.children.get(ch)
            if curr is None:
                return False
        return curr.is_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
        """
        curr = self.root
        for ch in prefix:
            curr = curr.children.get(ch)
            if curr is None:
                return False
        return True

# Your Trie object will be instantiated and called as such:
# obj = Trie()
# obj.insert(word)
# param_2 = obj.search(word)
# param_3 = obj.startsWith(prefix)