如何在C ++中从地图取消引用指向列表节点的指针？ LRU缓存

问题描述

此处的最小可复制示例：https://repl.it/@amejiarosario/lrc-cachecpp

我正在使用unordered_map和双向链接list在C ++上实现LRU缓存。每个链接列表节点都是一个数组[key,value]。 HashMap以整数作为键，值是指向链表中Node的指针/迭代器：

class LRUCache {
  int max;
  list<vector<int,int>> kvList;
  unordered_map<int,decltype(kvList)::iterator> lmap;
public:
  LRUCache(int capacity): max(capacity) {}

  int get(int key) {
    auto it = lmap.find(key);
    if (it == lmap.end()) return -1;
    put(key,(*it->second)[0]);
    return (*it->second)[0];
  }

  void put(int key,int value) {
    kvList.push_back({ key,value });
    if (lmap.find(key) != lmap.end()) kvList.erase(lmap.at(key));
    lmap[key] = prev(kvList.end());
  }
};

运行此代码时遇到一些问题。当我像初始化

LRUCache *lRUCache = new LRUCache(2);

我收到以下错误：

clang++-7 -pthread -std=c++17 -o main main.cpp
In file included from main.cpp:1:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/list:63:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/stl_list.h:60:
/usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/ext/alloc_traits.h:49:47: error: 
      type 'int' cannot be used prior to '::' because it has no members
template<typename _Alloc,typename = typename _Alloc::value_type>
                                              ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/stl_vector.h:83:35: note: 
      in instantiation of default argument for '__alloc_traits<int>' required
      here
      typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template
                                  ^~~~~~~~~~~~~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/stl_vector.h:339:30: note: 
      in instantiation of template class 'std::_Vector_base<int,int>'
      requested here
    class vector : protected _Vector_base<_Tp,_Alloc>
                             ^
main.cpp:16:12: note: in instantiation of template class
      'std::vector<int,int>' requested here
    if (it == lmap.end()) return -1;

if (it == lmap.end()) return -1;怎么了？

解决方法

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