LRU算法 C++

#pragma once

#include <list>
#include <unordered_map>
using namespace std;
class LRUCache
{
public:
    LRUCache(int capacity) : cap(capacity)
    {
        m.reserve(capacity);
        m.max_load_factor(0.75);
    }

    int get(int key)
    {
        auto it = m.find(key);
        if (it == m.cend())
            return -1;
        l.splice(l.begin(), l, it->second);
        return it->second->second;
    }

    void put(int key, int value)
    {
        auto it = m.find(key);
        if (it != m.cend())
        {
            l.erase(it->second);
        }
        else if (m.size() >= cap)
        {
            int k = l.rbegin()->first;
            l.pop_back();
            m.erase(k);
        }
        l.emplace_front(make_pair(key, value));
        m[key] = l.begin();
    }

private:
    int cap;
    list<pair<int, int>> l;
    unordered_map<int, list<pair<int, int>>::iterator> m;
};