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设计和构建一个“最近最少使用”缓存,该缓存会删除最近最少使用的项目。缓存应该从键映射到值(允许你插入和检索特定键对应的值),并在初始化时指定最大容量。当缓存被填满时,它应该删除最近最少使用的项目。
它应该支持以下操作: 获取数据 get 和 写入数据 put 。
获取数据 get(key) - 如果密钥 (key) 存在于缓存中,则获取密钥的值(总是正数),否则返回 -1。 写入数据 put(key, value) - 如果密钥不存在,则写入其数据值。当缓存容量达到上限时,它应该在写入新数据之前删除最近最少使用的数据值,从而为新的数据值留出空间。
示例:
LRUCache cache = new LRUCache( 2 /* 缓存容量 */ ); cache.put(1, 1); cache.put(2, 2); cache.get(1); // 返回 1 cache.put(3, 3); // 该操作会使得密钥 2 作废 cache.get(2); // 返回 -1 (未找到) cache.put(4, 4); // 该操作会使得密钥 1 作废 cache.get(1); // 返回 -1 (未找到) cache.get(3); // 返回 3 cache.get(4); // 返回 4
解法: 双向链表+Hash Table。 双向链表首尾设置哑结点,表头放置最近处理过的key,表尾放置很久以前处理过的key。 代码如下:
class LRUCache { public: struct Node{ int val; Node* pre; Node* next; Node(): val(-1), pre(nullptr), next(nullptr) {} Node(int x): val(x), pre(nullptr), next(nullptr) {} }; int c; Node* head = new Node(); Node* tail = new Node(); int len = 0; map<int, int> mp; LRUCache(int capacity) { c = capacity; head->next = tail; tail->pre = head; } void updatePositoin(int key) { Node* p = head; // find while (p->next != tail) { if (p->next->val == key) break; p = p->next; } // delete Node* target = p->next; p->next = target->next; target->next->pre = p; // insert target into head target->next = head->next; target->pre = head; head->next = target; target->next->pre = target; } int deleteTail() { int res = tail->pre->val; // delete old tail Node* tmp = tail->pre; tmp->pre->next = tail; tail->pre = tmp->pre; return res; } void append(int key) { Node* target = new Node(key); // insert target into head target->next = head->next; target->pre = head; head->next = target; target->next->pre = target; } int get(int key) { if (mp.find(key) != mp.end()) { updatePositoin(key); return mp[key]; } return -1; } void put(int key, int value) { if (mp.find(key) != mp.end()) { // update updatePositoin(key); } else { // append len++; if (len > c) { int tmp = deleteTail(); mp.erase(tmp); } append(key); } mp[key] = value; } }; /** * Your LRUCache object will be instantiated and called as such: * LRUCache* obj = new LRUCache(capacity); * int param_1 = obj->get(key); * obj->put(key,value); */
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设计和构建一个“最近最少使用”缓存,该缓存会删除最近最少使用的项目。缓存应该从键映射到值(允许你插入和检索特定键对应的值),并在初始化时指定最大容量。当缓存被填满时,它应该删除最近最少使用的项目。
它应该支持以下操作: 获取数据 get 和 写入数据 put 。
获取数据 get(key) - 如果密钥 (key) 存在于缓存中,则获取密钥的值(总是正数),否则返回 -1。
写入数据 put(key, value) - 如果密钥不存在,则写入其数据值。当缓存容量达到上限时,它应该在写入新数据之前删除最近最少使用的数据值,从而为新的数据值留出空间。
示例:
解法:
双向链表+Hash Table。
双向链表首尾设置哑结点,表头放置最近处理过的key,表尾放置很久以前处理过的key。
代码如下:
The text was updated successfully, but these errors were encountered: