设计搜索自动补全系统

// Java Stream solution for LeetCode problem 642: Design Search Autocomplete System
// 
// Problem Statement:
// Implement an autocomplete system using Java Streams for more concise code.
// This solution will still use a Trie data structure for efficiently storing
// and querying prefixes, but we'll leverage Streams for operations like sorting.
 
import java.util.*;
import java.util.stream.*;
 
class AutocompleteSystemStream {
    private class TrieNode {
        Map<Character, TrieNode> children = new HashMap<>();
        Map<String, Integer> counts = new HashMap<>();
        boolean isWord = false;
    }
    private TrieNode root = new TrieNode();
    private String currentSentence = "";
 
    public AutocompleteSystemStream(String[] sentences, int[] times) {
        for (int i = 0; i < sentences.length; i++) {
            add(sentences[i], times[i]);
        }
    }
 
    private void add(String sentence, int time) {
        TrieNode node = root;
        for (char c : sentence.toCharArray()) {
            node = node.children.computeIfAbsent(c, k -> new TrieNode());
            node.counts.put(sentence, node.counts.getOrDefault(sentence, 0) + time);
        }
        node.isWord = true;
    }
 
    public List<String> input(char c) {
        if (c == '#') {
            add(currentSentence, 1);
            currentSentence = "";
            return Collections.emptyList();
        }
        currentSentence += c;
        TrieNode node = root;
        for (char cc : currentSentence.toCharArray()) {
            if (!node.children.containsKey(cc)) {
                return Collections.emptyList();
            }
            node = node.children.get(cc);
        }
        return node.counts.entrySet().stream()
                .sorted((a, b) -> b.getValue().equals(a.getValue()) ? a.getKey().compareTo(b.getKey()) : b.getValue() - a.getValue())
                .limit(3)
                .map(Map.Entry::getKey)
                .collect(Collectors.toList());
    }
}