[leetCode]642. 設計搜尋自動補全系統

題目

字首樹

class AutocompleteSystem {
    private StringBuilder haveInput;
    private List<Pair<String, Integer>> ans;

    public AutocompleteSystem(String[] sentences, int[] times) {
        haveInput = new StringBuilder();
        ans = new ArrayList<>();
        root = new TrieNode();
        for (int i = 0; i < sentences.length; i++) {
            insert(sentences[i], times[i]);
        }
    }
    
    public List<String> input(char c) {
        ans.clear();
        List<String> res = new ArrayList<>();
        if (c == '#') {
            insert(haveInput.toString(), 1);
            haveInput.setLength(0);
        } else {
            haveInput.append(c);
            TrieNode node = searchNode(haveInput.toString());
            search(node);
            Collections.sort(ans, (o1, o2) -> {
                if (o1.getValue() == o2.getValue()) 
                    return o1.getKey().compareTo(o2.getKey());
                return o2.getValue().compareTo(o1.getValue());
            });
        
            for (int i = 0; i < Math.min(3, ans.size()); i++) {
                res.add(ans.get(i).getKey());
            }
        }
        return res;
    }

    private TrieNode root;

    class TrieNode {
        String sentence;
        int freq;
        Map<Character, TrieNode> children;
        TrieNode() {
            sentence = null;
            freq = 0;
            children = new HashMap<>();
        }
    }

    public void insert(String sentence, int time) {
        TrieNode cur = root;
        for (char c : sentence.toCharArray()) {
            TrieNode next = cur.children.computeIfAbsent(c, k -> new TrieNode());
            cur = next;
        }
        cur.freq += time;
        cur.sentence = sentence;
    }

    private TrieNode searchNode(String s) {
        TrieNode cur = root;
        for (char c : s.toCharArray()) {
            if (cur.children.containsKey(c)) {
                cur = cur.children.get(c);
            } else {
                return null;
            }
        }
        return cur;
    }

    private void search(TrieNode node) {
        if (node == null) return;
        if (node.sentence != null) {
            ans.add(new Pair(node.sentence, node.freq));
        }
        for (TrieNode child : node.children.values()) {
            search(child);
        }
    }
}

/**
 * Your AutocompleteSystem object will be instantiated and called as such:
 * AutocompleteSystem obj = new AutocompleteSystem(sentences, times);
 * List<String> param_1 = obj.input(c);
 */