129 lines
2.9 KiB
Markdown
129 lines
2.9 KiB
Markdown
# LRU
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[Leetcode 146. LRU Cache](https://leetcode.cn/problems/lru-cache/description/)
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Header:
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```cpp
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#ifndef S0146_LRU_CACHE_HPP
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#define S0146_LRU_CACHE_HPP
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#include <cstdlib>
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#include <unordered_map>
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class LRUCache {
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public:
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/**
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* @brief Least Recently Used Cache
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*
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* 这是一种常用的页面置换算法，选择最近最久未使用的页面予以淘汰
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*
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* @param capacity 容量，这是一个正整数
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*/
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LRUCache(int capacity);
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/**
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* @brief 读取数据
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*
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* @param key 数据对应的键值
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* @return 数据的值
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*/
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int get(int key);
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/**
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* @brief 放入对应的数据
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*
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* @param key 数据对应的键值
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* @param value 数据对应的值
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*/
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void put(int key, int value);
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private:
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struct CacheNode {
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int key;
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int value;
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CacheNode *next;
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CacheNode *prev;
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CacheNode(int key, int value)
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: key(key), value(value), next(nullptr), prev(nullptr){};
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CacheNode(int key, int value, CacheNode *next, CacheNode *prev)
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: key(key), value(value), next(next), prev(prev){};
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};
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CacheNode *head;
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CacheNode *tail;
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int capacity;
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std::unordered_map<int, CacheNode *> map; // 键值是 key，值是该节点的指针
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void moveToHead(CacheNode *node); // 将节点移动到头部
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};
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#endif
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```
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Source:
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```cpp
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#include "s0146_lru_cache.hpp"
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void LRUCache::moveToHead(CacheNode *node) {
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// 如果是头部节点
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if (node == head) return;
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// 如果不是头部节点，但是是尾部节点
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if (node == tail) tail = node->prev;
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// 处理该节点的前后两个节点的指针
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if (node->prev) node->prev->next = node->next;
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if (node->next) node->next->prev = node->prev;
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// 将该节点移动到头部
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node->prev = nullptr;
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node->next = head;
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// 处理头部节点
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head->prev = node;
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head = node;
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}
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LRUCache::LRUCache(int capacity) {
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this->capacity = capacity;
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head = nullptr;
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tail = nullptr;
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map = std::unordered_map<int, CacheNode *>();
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}
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int LRUCache::get(int key) {
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if (map.size() == 0) return -1;
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if (map.count(key) == 0) return -1;
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moveToHead(map[key]);
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return map[key]->value;
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}
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void LRUCache::put(int key, int value) {
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// 如果 key 已存在，则更新 value ，并将这个节点移动到头部
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if (map.count(key) == 1) {
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map[key]->value = value;
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moveToHead(map[key]);
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return;
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}
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// 否则创建该节点
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CacheNode *newNode = (CacheNode *)malloc(sizeof(CacheNode));
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newNode->value = value;
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newNode->key = key;
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newNode->next = head;
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newNode->prev = nullptr;
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// 处理头部节点
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if (head) head->prev = newNode;
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head = newNode;
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// 处理尾部节点
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if (map.size() == 0) tail = newNode;
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// 更新哈希表
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map[key] = newNode;
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// 如果容量已满
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if (map.size() > capacity) {
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// 更新尾部节点
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CacheNode *node = tail;
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if (tail->prev) {
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tail->prev->next = nullptr;
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tail = tail->prev;
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}
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// 移除该节点
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map.erase(node->key);
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free(node);
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}
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}
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```
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