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| class LFUCache {
public:
LFUCache(int capacity) : head(new Node(-1, 0, -1)), tail(new Node(-1, 0, INT_MAX)), size(0), capacity(capacity) {
head->next = tail;
tail->prev = head;
}
int get(int key) {
if(capacity == 0)
return -1;
if(!map.count(key))
return -1;
auto ret = map[key]->value;
int oldc = map[key]->count++;
if(oldc != map[key]->prev->count && oldc != map[key]->next->count)
location.erase(oldc);
else if(oldc == map[key]->prev->count && oldc != map[key]->next->count)
location[oldc] = map[key]->prev;
int c = oldc + 1;
if(c >= map[key]->next->count)
moveToNext(location[map[key]->next->count], map[key]);
if(c == map[key]->next->count)
moveToNext(location[c], map[key]);
location[c] = map[key];
return ret;
}
void put(int key, int value) {
if(capacity == 0)
return;
if(!map.count(key))
{
if(++size > capacity)
{
--size;
removeHead();
}
addToHead(key, value);
}else
{
map[key]->value = value;
int oldc = map[key]->count++;
if(oldc != map[key]->prev->count && oldc != map[key]->next->count)
location.erase(oldc);
else if(oldc == map[key]->prev->count && oldc != map[key]->next->count)
location[oldc] = map[key]->prev;
}
auto c = map[key]->count;
if(c >= map[key]->next->count)
moveToNext(location[map[key]->next->count], map[key]);
if(c == map[key]->next->count)
moveToNext(location[c], map[key]);
location[c] = map[key];
}
private:
struct Node
{
int key;
int count;
int value;
Node* prev;
Node* next;
Node(int key, int value, int count = 1) : key(key), value(value), count(count) {}
};
Node *head, *tail;
int size, capacity;
unordered_map<int, Node*> map;
unordered_map<int, Node*> location;
private:
void exchangeNearbyNodes(Node* n1, Node* n2)
{
n1->next = n2->next;
n2->next->prev = n1;
n2->next = n1;
n2->prev = n1->prev;
n1->prev->next = n2;
n1->prev = n2;
}
void removeHead()
{
if(head->next == tail)
return;
auto node = head->next;
head->next->next->prev = head;
head->next = head->next->next;
map.erase(node->key);
if(node->next->count != node->count)
location.erase(node->count);
delete node;
}
void addToHead(int key, int value)
{
auto node = new Node(key, value);
node->next = head->next;
head->next->prev = node;
head->next = node;
node->prev = head;
map.emplace(key, node);
}
void isolatedNode(Node* node)
{
node->prev->next = node->next;
node->next->prev = node->prev;
}
void moveToNext(Node* prev, Node* node)
{
isolatedNode(node);
node->next = prev->next;
node->prev = prev;
prev->next->prev = node;
prev->next = node;
}
};
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