【面试系列】LRU缓存

题意：
原题链接

代码：

struct DoubleListNode {
    
    
    DoubleListNode* prev, *next;
    int key;
    int val;
    DoubleListNode() : prev(NULL), next(NULL), key(-1), val(-1){
    
    }
    DoubleListNode(int key, int val) : prev(NULL), next(NULL), key(key), val(val){
    
    }
};

class LRUCache {
    
    
    
public:
    
    int size;
    int capacity;
    DoubleListNode *head, *tail;
    unordered_map<int, DoubleListNode*> hash;
    
    LRUCache(int _capacity) {
    
    
        size = 0;
        capacity = _capacity;
        head = new DoubleListNode();
        tail = new DoubleListNode();
        head->next = tail;
        tail->prev = head;
    }
    
    void addNode(DoubleListNode* node) {
    
    
        node->next = tail;
        node->prev = tail->prev;
        tail->prev->next = node;
        tail->prev = node;
    }
    
    void removeNode(DoubleListNode* node) {
    
    
        node->prev->next = node->next;
        node->next->prev = node->prev;
    }
    
    int get(int key) {
    
    
        if(!hash.count(key)) return -1;
        DoubleListNode *tmp = hash[key];
        removeNode(tmp);
        addNode(tmp);
        return tmp->val;
    }
    
    void put(int key, int value) {
    
    
        if(!hash.count(key)) {
    
    
            if(size >= capacity) {
    
    
                hash.erase(head->next->key);
                removeNode(head->next);
                --size;
            }
            DoubleListNode* node = new DoubleListNode(key, value);
            hash[key] = node;
            addNode(node);
            ++size;
        } else {
    
    
            removeNode(hash[key]);
            hash[key]->val = value;
            addNode(hash[key]);
        }
    }
};

/**
 * 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);
 */