LeetCode - LRU Cache

LRU Cache - Least Recently Used可以用一个list来实现（front为使用最久远的）

class LRUCache {
public:
    LRUCache(int capacity) {
        cap = capacity;
    }
    
    int get(int key) {
        auto it = m.find(key);
        if(it==m.end()) return -1;
        lru.splice(lru.begin(), lru, it->second);
        // m[key] = lru.begin(); no need to do this line
        return it->second->second;
    }
    
    void put(int key, int value) {
        auto it = m.find(key);
        if(it!=m.end()) lru.erase(m[key]);
        lru.push_front({key, value});
        m[key] = lru.begin();
        if(m.size()>cap){
            m.erase(lru.back().first);
            lru.pop_back();
        }
    }
private:
    int cap;
    unordered_map<int, list<pair<int,int>>::iterator> m;
    list<pair<int,int>> lru;
};

/**
 * 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);
 */