Created
December 6, 2019 09:04
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C++11 LRU Cache
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#include <list> | |
#include <unordered_map> | |
class LRUCache { | |
public: | |
LRUCache(int capacity) : capacity_(capacity) {} | |
int get(int key) { | |
auto it = used_.find(key); | |
if (it == used_.end()) { | |
return -1; | |
} | |
least_.splice(least_.begin(), least_, it->second); | |
return it->second->second; | |
} | |
void put(int key, int value) { | |
auto it = used_.find(key); | |
if (it != used_.end()) { | |
least_.splice(least_.begin(), least_, it->second); | |
it->second->second = value; | |
} else { | |
least_.push_front(std::make_pair(key, value)); | |
used_[key] = least_.begin(); | |
if (used_.size() > capacity_) { | |
used_.erase(least_.back().first); | |
least_.pop_back(); | |
} | |
} | |
} | |
private: | |
int capacity_; | |
std::list<std::pair<int, int>> least_; | |
std::unordered_map<int, decltype(least_)::iterator> used_; | |
}; | |
int main() { | |
LRUCache cache(2); | |
cache.put(1, 1); | |
cache.put(2, 2); | |
cache.get(1); // returns 1 | |
cache.put(3, 3); // evicts key 2 | |
cache.get(2); // returns -1 (not found) | |
cache.put(4, 4); // evicts key 1 | |
cache.get(1); // returns -1 (not found) | |
cache.get(3); // returns 3 | |
cache.get(4); // returns 4 | |
} |
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