720. 词典中最长的单词

题目链接	720. 词典中最长的单词
思路	Trie树的经典应用
题解链接	官方题解
关键点	构建Trie树
时间复杂度	\(O(\sum_{i}\#\text{word}_{i})\)
空间复杂度	\(O(\sum_{i}\#\text{word}_{i})\)

代码实现：

class Trie:
    def __init__(self):
        self.children = [None] * 26
        self.isEnd = False

    def insert(self, word):
        node = self
        for ch in word:
            ch = ord(ch) - ord("a")
            if not node.children[ch]:
                node.children[ch] = Trie()
            node = node.children[ch]
        node.isEnd = True

    def search(self, word):
        node = self
        for ch in word:
            ch = ord(ch) - ord("a")
            if node.children[ch] is None or not node.children[ch].isEnd:
                return False
            node = node.children[ch]
        return True


class Solution:
    def longestWord(self, words: List[str]) -> str:
        tree = Trie()
        for word in words:
            tree.insert(word)
        answer = ""
        for word in words:
            if tree.search(word) and (
                len(word) > len(answer) or len(word) == len(answer) and word < answer
            ):
                answer = word
        return answer