[hard]146. LRU Cache

最新推荐文章于 2025-12-02 18:04:47 发布

原创最新推荐文章于 2025-12-02 18:04:47 发布 · 282 阅读

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#LRU #map #leetcode

本文介绍了一种最少最近使用（LRU）缓存的数据结构设计与实现方法，该缓存支持get和set操作，并在达到容量限制时移除最少最近使用的项。通过使用三个映射表来维护数据及其时间关系。

146. LRU Cache

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

很简单，使用hash或者map维护数据和时间的关系

class LRUCache{
    map <int, int> data;
    map <int, int > timer;
    map <int, int> data_time;

    int cap, time;
public:
    LRUCache(int capacity) {
        cap = capacity;
        time = 0;
    }
    
    void timer_check() {
        while (0 == data_time.count(timer.begin() -> second) ||
            data_time[timer.begin() -> second] != timer.begin() -> first)
            timer.erase(timer.begin());
    }

    void check() {
        timer_check();
        while (data.size() > cap) {
            data.erase(timer.begin() -> second);
            data_time.erase(timer.begin() -> second);
            timer.erase(timer.begin());
            timer_check();
        }
    }
    
    int get(int key) {
        if (data.count(key)) {
            ++ time;
            timer[time] = key;
            data_time[key] = time;
            timer_check();
            return data[key];
        }
        return -1;
    }