Implement LRU cache

lru.cpp

#include <iostream>
#include <string>
#include <unordered_map>
#include <list>

using namespace std;

template <class K, class V> class LRU {
private:
	/* Members */
	unordered_map<K, pair<typename list<K>::iterator, V > > map;
	list<K> linkedList;
	int size;

	/* Private methods. */

	// Assume that key k doesn't exist in cache
	void add(K k, V v) {
		linkedList.push_front(k);
		map[k] = pair< list<K>::iterator, V >(linkedList.begin(), v);
	}

public:
	// constructor
	LRU(int size) {
		this->size = size;
	}

	void put(K k, V v) {
		// if key k exist - update
		if (map.count(k) > 0) {
			linkedList.erase(map[k].first);
		}
		else if (map.size() == size) { // max size, need to remove least recently used
			K last = linkedList.back();
			linkedList.pop_back();
			map.erase(last);
		}

		add(k,v);
	}

	V get(K k) {
		if (map.count(k) == 0) {
			return nullptr;
		}

		linkedList.erase(map[k].first);
		linkedList.push_front(k);
		map[k].first = linkedList.begin();
		return map[k].second;
	}

	void print() {
		cout << "Map: ";
		for ( auto& p: map ) {
			cout << p.first << ",";
		}
		cout << "\nList: ";
		for ( auto& l: linkedList ) {
			cout << l << ",";
		}
		cout << endl;
	}
};

int main() {
	LRU<int, string> lru(5);

	lru.put(1,"A");
	lru.put(2,"B");
	lru.put(3,"C");
	lru.put(4,"D");
	lru.put(5,"E");
	lru.put(2,"F");
	lru.put(6,"G");

	lru.print();
}