【leetcode】1032. Stream of Characters
题目如下:
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 somek >= 1
, the lastk
characters queried (in order from oldest to newest, including this letter just queried) spell one of the words in the given list.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 wordlistNote:
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.
解题思路:本题真对不起hard的级别,用字典树即可解决。首先在init的时候,把words中所有word逆置后存入字典树中;在query的时候,也有逆序的方式记录所有历史query过的值,同时判断其前缀是否存在于字典树中即可。
代码如下:
class TreeNode(object):
def __init__(self, x):
self.val = x
self.childDic = {}
self.isword = False class Trie(object):
dic = {}
def __init__(self):
"""
Initialize your data structure here.
"""
self.root = TreeNode(None)
self.dic = {} def insert(self,word):
node = self.root
for i in word:
if i not in node.childDic:
node.childDic[i] = TreeNode(i)
node = node.childDic[i]
node.isword = True
def isExist(self,word):
node = self.root
for i in word:
if i in node.childDic:
node = node.childDic[i]
if node.isword == True:
return True
else:
return False class 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.q
return self.t.isExist(self.q)
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