題目如下：

Implement the?StreamChecker?class as follows:

• StreamChecker(words): Constructor, init the data structure with the given words.
• query(letter): returns true if and only if for some?k >= 1, the last?k?characters queried (in order from oldest to newest, including this letter just queried) spell one of the words in the given list.

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Example:

StreamChecker streamChecker = new StreamChecker(["cd","f","kl"]); // init the dictionary. streamChecker.query('a'); // return false streamChecker.query('b'); // return false streamChecker.query('c'); // return false streamChecker.query('d'); // return true, because 'cd' is in the wordlist streamChecker.query('e'); // return false streamChecker.query('f'); // return true, because 'f' is in the wordlist streamChecker.query('g'); // return false streamChecker.query('h'); // return false streamChecker.query('i'); // return false streamChecker.query('j'); // return false streamChecker.query('k'); // return false streamChecker.query('l'); // return true, because 'kl' is in the wordlist

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Note:

• 1 <= words.length <= 2000
• 1 <= words[i].length <= 2000
• Words will only consist of lowercase English letters.
• Queries will only consist of lowercase English letters.
• The number of queries is at most?40000.

解題思路：本題真對不起hard的級別，用字典樹即可解決。首先在init的時候，把words中所有word逆置后存入字典樹中；在query的時候，也有逆序的方式記錄所有歷史query過的值，同時判斷其前綴是否存在于字典樹中即可。

代碼如下：

class TreeNode(object):def __init__(self, x):self.val = xself.childDic = {}self.isword = Falseclass Trie(object):dic = {}def __init__(self):"""Initialize your data structure here."""self.root = TreeNode(None)self.dic = {}def insert(self,word):node = self.rootfor i in word:if i not in node.childDic:node.childDic[i] = TreeNode(i)node = node.childDic[i]node.isword = Truedef isExist(self,word):node = self.rootfor i in word:if i in node.childDic:node = node.childDic[i]if node.isword == True:return Trueelse:return Falseclass StreamChecker(object):q = ''def __init__(self, words):""":type words: List[str]"""self.t = Trie()for w in words:self.t.insert(w[::-1])def query(self, letter):""":type letter: str:rtype: bool"""#letter = letter[::-1]self.q = letter + self.qreturn self.t.isExist(self.q)

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轉載于:https://www.cnblogs.com/seyjs/p/10765511.html

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