题目描述:
LeetCode 642. Design Search Autocomplete System
Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character '#'
). For each character they type except '#', you need to return the top 3 historical hot sentences that have prefix the same as the part of sentence already typed. Here are the specific rules:
- The hot degree for a sentence is defined as the number of times a user typed the exactly same sentence before.
- The returned top 3 hot sentences should be sorted by hot degree (The first is the hottest one). If several sentences have the same degree of hot, you need to use ASCII-code order (smaller one appears first).
- If less than 3 hot sentences exist, then just return as many as you can.
- When the input is a special character, it means the sentence ends, and in this case, you need to return an empty list.
Your job is to implement the following functions:
The constructor function:
AutocompleteSystem(String[] sentences, int[] times):
This is the constructor. The input is historical data. Sentences
is a string array consists of previously typed sentences. Times
is the corresponding times a sentence has been typed. Your system should record these historical data.
Now, the user wants to input a new sentence. The following function will provide the next character the user types:
List<String> input(char c):
The input c
is the next character typed by the user. The character will only be lower-case letters ('a'
to 'z'
), blank space (' '
) or a special character ('#'
). Also, the previously typed sentence should be recorded in your system. The output will be the top 3 historical hot sentences that have prefix the same as the part of sentence already typed.
Example:
Operation: AutocompleteSystem(["i love you", "island","ironman", "i love leetcode"], [5,3,2,2])
The system have already tracked down the following sentences and their corresponding times:
"i love you"
: 5
times
"island"
: 3
times
"ironman"
: 2
times
"i love leetcode"
: 2
times
Now, the user begins another search:
Operation: input('i')
Output: ["i love you", "island","i love leetcode"]
Explanation:
There are four sentences that have prefix "i"
. Among them, "ironman" and "i love leetcode" have same hot degree. Since ' '
has ASCII code 32 and 'r'
has ASCII code 114, "i love leetcode" should be in front of "ironman". Also we only need to output top 3 hot sentences, so "ironman" will be ignored.
Operation: input(' ')
Output: ["i love you","i love leetcode"]
Explanation:
There are only two sentences that have prefix "i "
.
Operation: input('a')
Output: []
Explanation:
There are no sentences that have prefix "i a"
.
Operation: input('#')
Output: []
Explanation:
The user finished the input, the sentence "i a"
should be saved as a historical sentence in system. And the following input will be counted as a new search.
Note:
- The input sentence will always start with a letter and end with '#', and only one blank space will exist between two words.
- The number of complete sentences that to be searched won't exceed 100. The length of each sentence including those in the historical data won't exceed 100.
- Please use double-quote instead of single-quote when you write test cases even for a character input.
- Please remember to RESET your class variables declared in class AutocompleteSystem, as static/class variables are persisted across multiple test cases. Please see here for more details.
题目大意:
设计搜索自动完成系统
包含如下两个方法:
构造方法:
AutocompleteSystem(String[] sentences, int[] times): 输入句子sentences,及其出现次数times
输入方法:
List<String> input(char c): 输入字符c可以是26个小写英文字母,也可以是空格,以'#'结尾。返回输入字符前缀对应频率最高的至多3个句子,频率相等时按字典序排列。
解题思路:
Trie(字典树)
利用字典树记录所有出现过的句子集合,利用字典保存每个句子出现的次数。
Python代码:
class TrieNode:
def __init__(self):
self.children = dict()
self.sentences = set()
class AutocompleteSystem(object):
def __init__(self, sentences, times):
"""
:type sentences: List[str]
:type times: List[int]
"""
self.buffer = ''
self.stimes = collections.defaultdict(int)
self.trie = TrieNode()
for s, t in zip(sentences, times):
self.stimes[s] = t
self.addSentence(s)
self.tnode = self.trie
def input(self, c):
"""
:type c: str
:rtype: List[str]
"""
ans = []
if c != '#':
self.buffer += c
if self.tnode: self.tnode = self.tnode.children.get(c)
if self.tnode: ans = sorted(self.tnode.sentences, key=lambda x: (-self.stimes[x], x))[:3]
else:
self.stimes[self.buffer] += 1
self.addSentence(self.buffer)
self.buffer = ''
self.tnode = self.trie
return ans
def addSentence(self, sentence):
node = self.trie
for letter in sentence:
child = node.children.get(letter)
if child is None:
child = TrieNode()
node.children[letter] = child
node = child
child.sentences.add(sentence)
# Your AutocompleteSystem object will be instantiated and called as such:
# obj = AutocompleteSystem(sentences, times)
# param_1 = obj.input(c)
本文链接:http://bookshadow.com/weblog/2017/07/16/leetcode-design-search-autocomplete-system/
请尊重作者的劳动成果,转载请注明出处!书影博客保留对文章的所有权利。