208. Implement Trie (Prefix Tree)

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.

解题要点：

大致和#211一样，根据大神211题解法稍微改动了一下。

class Trie(object):

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

    def insert(self, word):
        """
        Inserts a word into the trie.
        :type word: str
        :rtype: None
        """
        node = self.root
        for c in word:
            node = node.setdefault(c, {})
        node[None] = None
        # print self.root

    def search(self, word):
        """
        Returns if the word is in the trie.
        :type word: str
        :rtype: bool
        """
        def find(word, root):
            if not word:
                return None in root
            c, w = word[0], word[1:]
            return c in root and find(w, root[c])
        return find(word, self.root)

    def startsWith(self, prefix):
        """
        Returns if there is any word in the trie that starts with the given prefix.
        :type prefix: str
        :rtype: bool
        """
        def find(word, root):
            if not word:
                return True
            c, w = word[0], word[1:]
            return c in root and find(w, root[c])
        return find(prefix, self.root)

# 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)