146. LRU 缓存

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class LRUCache {
public:
    LRUCache(int capacity)
        :_capacity(capacity)
    {}

    int get(int key) {
        auto it = _unorderedMap.find(key);
        if(it != _unorderedMap.end()){
            _list.splice(_list.begin(), _list, it->second);
            return it->second->second;
        }else{
            return -1;
        }
    }
    
    void put(int key, int value) {
        auto it = _unorderedMap.find(key);
        if(it != _unorderedMap.end()){
            it->second->second = value;
            _list.splice(_list.begin(), _list, it->second);
        }else{
            if(_capacity == _list.size()){//满了
                auto deletenode = _list.back();
                _unorderedMap.erase(_unorderedMap.find(deletenode.first));
                _list.pop_back();
            }
            _list.push_front(pair<int, int>(key, value));
            _unorderedMap[key] = _list.begin();
        }
    }
private:
    int _capacity;
    list<pair<int, int>> _list;
    unordered_map<int, list<pair<int, int>>::iterator> _unorderedMap;
};