LRU cache

class LRUCache {
public:
    int size;
    list<int> lru;                              // MRU ... LRU
    unordered_map<int, list<int>::iterator> mp; // key -> iterator
    unordered_map<int, int> kv;
    LRUCache(int capacity) : size(capacity) {}

    int get(int key) {
        if (kv.count(key) == 0) return -1;
        updateLRU(key);
        return kv[key];
    }

    void put(int key, int value) {
        if (kv.size() == size && kv.count(key) == 0)evict();
        updateLRU(key);
        kv[key] = value;
    }
    void updateLRU(int key) {
        if (kv.count(key))lru.erase(mp[key]);
        lru.push_front(key);
        mp[key] = lru.begin();
    }
    void evict() {
        mp.erase(lru.back());
        kv.erase(lru.back());
        lru.pop_back();
    }
};