642. Design Search Autocomplete System 用trie树维持top3 list

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 the sentences and times arrays.
• List<String> input(char c) This indicates that the user typed the character c.
  • Returns an empty array [] if c == '#' 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 than 3 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.

 

半懂不懂，随便抄抄吧

class AutocompleteSystem {
    private HashMap<String, Integer> map;
    private StringBuilder sb;
    private TrieNode root;
    private TrieNode current;

    public AutocompleteSystem(String[] sentences, int[] times) {
        map = new HashMap<>();
        sb = new StringBuilder();
        root = new TrieNode();
        current = root;
        
        for (int i = 0; i < sentences.length; i++) {
            map.put(sentences[i], times[i]);
            root.add(sentences[i], 0);
        }
    }
    
    //每次input都返回top 3
    public List<String> input(char c) {
        if (c == '#') {
            String str = sb.toString();
            map.put(str, map.getOrDefault(str, 0) + 1);
            root.add(str, 0);
            sb = new StringBuilder();
            current = root;
            return new ArrayList<>();
        }
        sb.append(c);
        current = current.getNext(c);
        return current.top3;
    }
    
    private class TrieNode {
        private List<String> top3;
        private TrieNode[] next;
        
        private TrieNode() {
            this.top3 = new ArrayList<>();
            this.next = new TrieNode[27];
        }
        
        //每次add的时候都sort
        private void add(String s, int start) {
            if (!top3.contains(s)) top3.add(s);
            Collections.sort(top3, (a, b) -> {
                if (map.get(a) == map.get(b)) return a.compareTo(b);
                return map.get(b) - map.get(a);
            });
            if (top3.size() > 3) top3.remove(top3.size() - 1);
            if (start == s.length()) return;
            getNext(s.charAt(start)).add(s, start + 1);
        }
        
        private TrieNode getNext(char ch) {
            int index = ch == ' ' ? 26 : ch - 'a';
            if (next[index] == null) next[index] = new TrieNode();
            return next[index];
        }
    }
}