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 3historical hot sentences that have prefix the same as the part of sentence already typed. Here are the specific rules:

1. The hot degree for a sentence is defined as the number of times a user typed the exactly same sentence before.
2. 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).
3. If less than 3 hot sentences exist, then just return as many as you can.
4. 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. 

class AutocompleteSystem {
    private final Map<String, Integer> cache = new HashMap<String, Integer>();
    private String input = "";

    public AutocompleteSystem(String[] sentences, int[] times) {
        for (int i = 0; i < sentences.length; i++) {
            cache.put(sentences[i], times[i]);
        }
    }

    public List<String> input(char c) {
        if (c == '#') {
            Integer count = cache.getOrDefault(input, 0);
            cache.put(input, ++count);
            input = "";
            return Collections.emptyList();
        }

        input += c;
        return cache.entrySet().stream()
                .filter(e -> e.getKey().startsWith(input))
                .sorted(Map.Entry.<String, Integer>comparingByValue(Comparator.reverseOrder())
                        .thenComparing(Map.Entry.comparingByKey()))
                .limit(3)
                .map(Map.Entry::getKey)
                .collect(Collectors.toCollection(ArrayList::new));
    }
}

 

class AutocompleteSystem {
    class TrieNode {
        Map<Character, TrieNode> children;
        Map<String, Integer> counts;
        boolean isWord;

        public TrieNode() {
            children = new HashMap<>();
            counts = new HashMap<>();
            isWord = false;
        }
    }

    TrieNode root;
    String prefix;

    public AutocompleteSystem(String[] sentences, int[] times) {
        root = new TrieNode();
        prefix = "";
        for (int i = 0; i < sentences.length; i++) {
            add(sentences[i], times[i]);
        }
    }

    private void add(String s, int count) {
        TrieNode cur = root;
        for (char c : s.toCharArray()) {
            TrieNode next = cur.children.get(c);
            if (next == null) {
                next = new TrieNode();
                cur.children.put(c, next);
            }
            cur = next;
            cur.counts.put(s, cur.counts.getOrDefault(s, 0) + count);
        }
        cur.isWord = true;
    }

    public List<String> input(char c) {
        if (c == '#') {
            add(prefix, 1);
            prefix = "";
            return new ArrayList<String>();
        }

        prefix = prefix + c;
        TrieNode cur = root;
        for (char ch : prefix.toCharArray()) {
            TrieNode next = cur.children.get(ch);
            if (next == null) {
                return new ArrayList<String>();
            }
            cur = next;
        }

        PriorityQueue<Map.Entry<String, Integer>> pq = new PriorityQueue<>((a,
                b) -> (a.getValue() == b.getValue() ? a.getKey().compareTo(b.getKey()) : b.getValue() - a.getValue()));
        for (Map.Entry<String, Integer> entry : cur.counts.entrySet()) {
            pq.add(entry);
        }

        List<String> res = new ArrayList<>();
        for (int i = 0; i < 3 && !pq.isEmpty(); i++) {
            res.add(pq.poll().getKey());
        }
        return res;
    }
}