2022.03.18 - NC071.BM101 设计LFU缓存结构

1. 题目2. 思路

(1) 哈希表+优先队列 3. 代码 1. 题目

哈希表count存储key和调用该key的次数和时间，哈希表data存储真正的数据，优先队列存储key，按照调用次数从小到大排序，调用次数相等时，按照调用时间从小到大排序。 3. 代码

import java.util.ArrayList;
import java.util.HashMap;
import java.util.PriorityQueue;

public class Solution {
    class Node {
        public int count;
        public int time;

        public Node(int count, int time) {
            this.count = count;
            this.time = time;
        }
    }

    
    public int[] LFU(int[][] operators, int k) {
        HashMap count = new HashMap<>();
        HashMap data = new HashMap<>();
        PriorityQueue minHeap = new PriorityQueue<>((o1, o2) -> Integer.compare(count.get(o1).count, count.get(o2).count) == 0 ?
                Integer.compare(count.get(o1).time, count.get(o2).time) : Integer.compare(count.get(o1).count, count.get(o2).count));
        ArrayList list = new ArrayList<>();
        int time = 0;
        for (int[] operator : operators) {
            if (operator[0] == 1) {
                int key = operator[1];
                int value = operator[2];
                if (data.size() == k) {
                    int removeKey = minHeap.poll();
                    count.remove(removeKey);
                    data.remove(removeKey);
                }
                data.put(key, value);
                if (count.containsKey(key)) {
                    Node node = new Node(count.get(key).count + 1, time++);
                    count.put(key, node);
                    minHeap.remove(key);
                    minHeap.offer(key);
                } else {
                    Node node = new Node(1, time++);
                    count.put(key, node);
                    minHeap.offer(key);
                }
            } else {
                int key = operator[1];
                if (data.containsKey(key)) {
                    list.add(data.get(key));
                    if (count.containsKey(key)) {
                        Node node = new Node(count.get(key).count + 1, time++);
                        count.put(key, node);
                        minHeap.remove(key);
                        minHeap.offer(key);
                    } else {
                        Node node = new Node(1, time++);
                        count.put(key, node);
                        minHeap.offer(key);
                    }
                } else {
                    list.add(-1);
                }
            }
        }
        int n = list.size();
        int[] res = new int[n];
        for (int i = 0; i < n; i++) {
            res[i] = list.get(i);
        }
        return res;
    }
}