字典树、树的遍历、二叉查找树_遍历字典树-优快云博客

本文链接：https://blog.youkuaiyun.com/solumin/article/details/97522559

本文详细介绍了数据结构中的字典树（前缀树），包括其概念和应用。接着讨论了树的遍历方法，如前序、中序和后续遍历。还探讨了如何计算树的高度和节点数量。最后，文章讲解了二叉查找树的特性，并阐述了如何在二叉查找树中查找第k小的元素。

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字典树前缀树

"""
一、题目
    实现一个字典树or前缀树，包含insert、search和startswith功能
"""


class Node():
    def __init__(self):
        self.childs = [None] * 26
        self.isLeaf = False


class Trie(object):
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.root = Node()

    def insert(self, word):
        """
        Inserts a word into the trie.
        :type word: str
        :rtype: void
        """
        self.inserthelper(word, self.root)

    def inserthelper(self, word, node):
        if node == Node:
            return
        if len(word) == 0:
            node.isLeaf = True
            return
        index = ord(word[0]) - ord('a')
        if node.childs[index] is None:
            node.childs[index] = Node()
        self.inserthelper(word[1:], node.childs[index])

    def search(self, word):
        """
        Returns if the word is in the trie.
        :type word: str
        :rtype: bool
        """
        return self.searchhepler(word, self.root)

    def searchhepler(self, word, node):
        if node is None:
            return False
        if len(word) == 0:
            return node.isLeaf
        index = ord(word[0]) - ord('a')
        return self.searchhepler(word[1:], node.childs[index])

    def startsWith(self, prefix):
        """
        Returns if there is any word in the trie that starts with the given prefix.
        :type prefix: str
        :rtype: bool
        """
        return self.startsWithhelper(prefix, self.root)

    def startsWithhelper(self, prefix, node):
        if node is None:
            return False
        if len(prefix) == 0:
            return True
        index = ord(prefix