Cinte's Leetcode Record
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460. LFU 缓存

Posted on Edited on In Disqus:
Symbols count in article: 5.9k Reading time ≈ 5 mins.

460. LFU 缓存

自己维护一个双向链表

记录每个count的值的最后一位是哪个

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class LFUCache {
public:
    LFUCache(int capacity) : head(new Node(-1, 0, -1)), tail(new Node(-1, 0, INT_MAX)), size(0), capacity(capacity) {
        head->next = tail;
        tail->prev = head;
    }
    
    int get(int key) {
        if(capacity == 0)
            return -1;
        if(!map.count(key))
            return -1;
        auto ret = map[key]->value;
        int oldc = map[key]->count++;
        if(oldc != map[key]->prev->count && oldc != map[key]->next->count)
            location.erase(oldc);
        else if(oldc == map[key]->prev->count && oldc != map[key]->next->count)
            location[oldc] = map[key]->prev;
        int c = oldc + 1;
        if(c >= map[key]->next->count)
            moveToNext(location[map[key]->next->count], map[key]);
        if(c == map[key]->next->count)
            moveToNext(location[c], map[key]);
        location[c] = map[key];
        return ret;
    }
    
    void put(int key, int value) {
        if(capacity == 0)
            return;
        if(!map.count(key))
        {
            if(++size > capacity)
            {
                --size;
                removeHead();
            }
            addToHead(key, value);
        }else
        {
            map[key]->value = value;
            int oldc = map[key]->count++;
            if(oldc != map[key]->prev->count && oldc != map[key]->next->count)
                location.erase(oldc);
            else if(oldc == map[key]->prev->count && oldc != map[key]->next->count)
                location[oldc] = map[key]->prev;
        }
        auto c = map[key]->count;
        if(c >= map[key]->next->count)
            moveToNext(location[map[key]->next->count], map[key]);
        if(c == map[key]->next->count)
            moveToNext(location[c], map[key]);
        location[c] = map[key];
    }
private:
    struct Node
    {
        int key;
        int count;
        int value;
        Node* prev;
        Node* next;
        Node(int key, int value, int count = 1) : key(key), value(value), count(count) {}
    };
    Node *head, *tail;
    int size, capacity;
    unordered_map<int, Node*> map;
    unordered_map<int, Node*> location;
private:
    void exchangeNearbyNodes(Node* n1, Node* n2)
    {
        n1->next = n2->next;
        n2->next->prev = n1;
        n2->next = n1;
        n2->prev = n1->prev;
        n1->prev->next = n2;
        n1->prev = n2;
    }
    void removeHead()
    {
        if(head->next == tail)
            return;
        auto node = head->next;
        head->next->next->prev = head;
        head->next = head->next->next;
        map.erase(node->key);
        if(node->next->count != node->count)
            location.erase(node->count);
        delete node;
    }
    void addToHead(int key, int value)
    {
        auto node = new Node(key, value);
        node->next = head->next;
        head->next->prev = node;
        head->next = node;
        node->prev = head;
        map.emplace(key, node);
    }
    void isolatedNode(Node* node)
    {
        node->prev->next = node->next;
        node->next->prev = node->prev;
    }
    void moveToNext(Node* prev, Node* node)
    {
        isolatedNode(node);
        node->next = prev->next;
        node->prev = prev;
        prev->next->prev = node;
        prev->next = node;
    }
};

/**
 * Your LFUCache object will be instantiated and called as such:
 * LFUCache* obj = new LFUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */

get: O(1)

put: O(1)

使用红黑树(c++中的set)
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class LFUCache {
public:
    LFUCache(int capacity) : time(0), capacity(capacity) {

    }
    
    int get(int key) {
        if(capacity == 0)
            return -1;
        if(!map.count(key))
            return -1;
        set.erase(map[key]);
        map[key].time = ++time;
        ++map[key].count;
        set.insert(map[key]);
        return map[key].value;
    }
    
    void put(int key, int value) {
        if(capacity == 0)
            return;
        if(map.count(key))
        {
            set.erase(map[key]);
            map[key].time = ++time;
            ++map[key].count;
            map[key].value = value;
            set.insert(map[key]);
        }else
        {
            if(map.size() == capacity)
            {
                auto node = set.begin();
                map.erase(node->key);
                set.erase(node);
            }
            Node node{key, value, 1, ++time};
            map.emplace(key, node);
            set.insert(std::move(node));
        }
    }
private:
    struct Node
    {
        int key;
        int value;
        int count;
        int time;
        Node() = default;
        Node(int key, int value, int count, int time) : key(key), value(value), count(count), time(time) {}
        bool operator < (const Node& rhs) const
        {
            return count == rhs.count ? time < rhs.time : count < rhs.count;
        }
    };
    int time;
    unordered_map<int, Node> map;
    set<Node> set;
    int capacity;
};

/**
 * Your LFUCache object will be instantiated and called as such:
 * LFUCache* obj = new LFUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */

get: O(logn)

put: O(logn)

使用双哈希表
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class LFUCache {
public:
    LFUCache(int capacity) : capacity(capacity), minFreq(1) {

    }
    
    int get(int key) {
        if(capacity == 0)
            return -1;
        if(!map.count(key))
            return -1;
        auto it = map[key];
        auto count = it->count;
        auto value = it->value;
        freq[count].erase(it);
        if(freq[count].size() == 0)
        {
            freq.erase(count);
            if(count == minFreq)
                ++minFreq;
        }
        ++count;
        freq[count].push_front(Node(key, value, count));
        map[key] = freq[count].begin();
        return value;
    }
    
    void put(int key, int value) {
        if(capacity == 0)
            return;
        if(!map.count(key))
        {
            if(map.size() == capacity)
            {
                auto it = --freq[minFreq].end(); // 不是随机迭代器，不能用-1
                map.erase(it->key);
                freq[minFreq].pop_back();
                if(freq[minFreq].size() == 0)
                    freq.erase(minFreq);
            }
            freq[1].push_front(Node(key, value, 1));
            map.emplace(key, freq[1].begin());
            minFreq = 1;
        }else
        {
            auto it = map[key];
            auto count = it->count;
            freq[count].erase(it);
            if(freq[count].size() == 0)
            {
                freq.erase(count);
                if(count == minFreq)
                    ++minFreq;
            }
            ++count;
            freq[count].push_front(Node(key, value, count));
            map[key] = freq[count].begin();
        }
    }
private:
    struct Node
    {
        int key;
        int value;
        int count;
        Node(int key, int value, int count) : key(key), value(value), count(count) {}
    };
    unordered_map<int, list<Node>::iterator> map;
    unordered_map<int, list<Node>> freq;
    int capacity;
    int minFreq;
};

/**
 * Your LFUCache object will be instantiated and called as such:
 * LFUCache* obj = new LFUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */