0642. Design Search Autocomplete System
https://leetcode.com/problems/design-search-autocomplete-system
Description
Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character '#'
).
You are given a string array sentences
and an integer array times
both of length n
where sentences[i]
is a previously typed sentence and times[i]
is the corresponding number of times the sentence was typed. For each input character except '#'
, return the top 3
historical hot sentences that have the same prefix as the part of the 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 hot degree, use ASCII-code order (smaller one appears first).If less than
3
hot sentences exist, 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.
Implement the AutocompleteSystem
class:
AutocompleteSystem(String[] sentences, int[] times)
Initializes the object with thesentences
andtimes
arrays.List<String> input(char c)
This indicates that the user typed the characterc
.Returns an empty array
[]
ifc == '#'
and stores the inputted sentence in the system.Returns the top
3
historical hot sentences that have the same prefix as the part of the sentence already typed. If there are fewer than3
matches, return them all.
Example 1:
**Input**
["AutocompleteSystem", "input", "input", "input", "input"]
[[["i love you", "island", "iroman", "i love leetcode"], [5, 3, 2, 2]], ["i"], [" "], ["a"], ["#"]]
**Output**
[null, ["i love you", "island", "i love leetcode"], ["i love you", "i love leetcode"], [], []]
**Explanation**
AutocompleteSystem obj = new AutocompleteSystem(["i love you", "island", "iroman", "i love leetcode"], [5, 3, 2, 2]);
obj.input("i"); // return ["i love you", "island", "i love leetcode"]. 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.
obj.input(" "); // return ["i love you", "i love leetcode"]. There are only two sentences that have prefix "i ".
obj.input("a"); // return []. There are no sentences that have prefix "i a".
obj.input("#"); // return []. 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.
Constraints:
n == sentences.length
n == times.length
1 <= n <= 100
1 <= sentences[i].length <= 100
1 <= times[i] <= 50
c
is a lowercase English letter, a hash'#'
, or space' '
.Each tested sentence will be a sequence of characters
c
that end with the character'#'
.Each tested sentence will have a length in the range
[1, 200]
.The words in each input sentence are separated by single spaces.
At most
5000
calls will be made toinput
.
ac
so ugly. Don't you need to consider the time complexity? whey not just maintain 3 sentence in a trie node. I try to use priorityqueue in each trie node, but just can't update as expected.
class AutocompleteSystem {
TrieNode root;
TrieNode r;
StringBuilder sb; // record input
public AutocompleteSystem(String[] sentences, int[] times) {
root = new TrieNode();
r = root;
sb = new StringBuilder();
// build trie
for (int i = 0; i < sentences.length; i++) {
build(sentences[i], times[i]);
}
}
public List<String> input(char c) {
List<String> res = new ArrayList<>();
if (c == '#') { // end input
String newSentence = sb.toString();
// update trie and frequency
build(newSentence, 1);
r = root; // reset for next input
sb.setLength(0);
return res;
}
// record input, add when input finish
sb.append(c);
if (r == null) return res;
int pos = c == ' ' ? 0 : c - 'a' + 1;
r = r.next[pos];
if (r != null) {
// get sentences
PriorityQueue<Map.Entry<String,Integer>> tmp = new PriorityQueue<Map.Entry<String,Integer>>((a, b) -> {
return a.getValue() != b.getValue() ? b.getValue() - a.getValue() : a.getKey().compareTo(b.getKey());
});
for (Map.Entry<String,Integer> e : r.predict.entrySet()) {
tmp.offer(e);
}
for (int i = 0; i < 3 && !tmp.isEmpty(); i++) {
Map.Entry<String,Integer> entry = tmp.poll();
res.add(entry.getKey());
}
}
return res;
}
private void build(String s, int time) {
TrieNode rt = root;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
int pos = c == ' ' ? 0 : c - 'a' + 1;
if (rt.next[pos] == null) rt.next[pos] = new TrieNode();
rt = rt.next[pos];
rt.predict.put(s, rt.predict.getOrDefault(s, 0) + time);
}
}
}
class TrieNode {
TrieNode[] next;
Map<String, Integer> predict;
public TrieNode() {
next = new TrieNode[27]; // frist is " " space
predict = new HashMap<>();
}
}
/**
* Your AutocompleteSystem object will be instantiated and called as such:
* AutocompleteSystem obj = new AutocompleteSystem(sentences, times);
* List<String> param_1 = obj.input(c);
*/
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