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/**

*

*/

public class LFUCache {

private FreqNode head;

private Map<Integer, FreqNode> freqMap = new HashMap<>();

private Map<Integer, ItemNode> itemMap = new HashMap<>();

private int capacity;

public LFUCache(int capacity) {

this.capacity = capacity;

this.head = new FreqNode();

this.head.next = this.head;

this.head.prev = this.head;

}

public int get(int key) {

if (!this.itemMap.containsKey(key)) return -1;

ItemNode item = this.itemMap.get(key);

updateNodeFreq(item);

return item.val;

}

private void updateNodeFreq(ItemNode item) {

dislinkNode(item);

Integer freq = item.freq;

item.freq++;

FreqNode currFreqNode = freqMap.get(freq);

FreqNode newFreqNode = freqMap.get(freq+1);

if (newFreqNode == null) {

newFreqNode = new FreqNode(freq+1);

freqMap.put(freq+1, newFreqNode);

addAfter(currFreqNode, newFreqNode);

}

addBefore(newFreqNode.itemHead, item);

if (itemNodeIsEmpty(currFreqNode.itemHead)) {

removeNode(currFreqNode);

}

}

private boolean itemNodeIsEmpty(ItemNode node) {

return node.next == node;

}

private void removeNode(FreqNode node) {

dislinkNode(node);

this.freqMap.remove(node.freq);

}

private void removeNode(ItemNode node) {

dislinkNode(node);

this.itemMap.remove(node.key);

}

private void dislinkNode(FreqNode node) {

node.prev.next = node.next;

node.next.prev = node.prev;

}

private void dislinkNode(ItemNode node) {

node.prev.next = node.next;

node.next.prev = node.prev;

}

private void addAfter(FreqNode currNode, FreqNode newNode) {

newNode.next = currNode.next;

newNode.prev = currNode;

currNode.next.prev = newNode;

currNode.next = newNode;

}

private void addAfter(ItemNode currNode, ItemNode newNode) {

newNode.next = currNode.next;

newNode.prev = currNode;

currNode.next.prev = newNode;

currNode.next = newNode;

}

private void addBefore(ItemNode currNode, ItemNode newNode) {

newNode.next = currNode;

newNode.prev = currNode.prev;

currNode.prev.next = newNode;

currNode.prev = newNode;

}

public void put(int key, int value) {

if (this.capacity == 0) return;

if (this.itemMap.containsKey(key)) {

ItemNode item = this.itemMap.get(key);

item.val = value;

updateNodeFreq(item);

return;

}

if (this.itemMap.size() == this.capacity) {

FreqNode first = this.head.next;

ItemNode toBeRemoved = first.itemHead.next;

removeNode(toBeRemoved);

if (itemNodeIsEmpty(first.itemHead)) {

removeNode(first);

}

}

FreqNode newFreqNode = freqMap.get(1);

if (newFreqNode == null) {

newFreqNode = new FreqNode(1);

freqMap.put(1, newFreqNode);

addAfter(this.head, newFreqNode);

}

ItemNode newItem = new ItemNode(key, value, 1);

addBefore(newFreqNode.itemHead, newItem);

this.itemMap.put(key, newItem);

}

private ItemNode newItemHead() {

ItemNode head = new ItemNode();

head.prev = head;

head.next = head;

return head;

}

class ItemNode extends Node {

ItemNode next;

ItemNode prev;

int key;

int val;

int freq;

ItemNode(int key, int val, int freq) {

this.key = key;

this.val = val;

this.freq = freq;

}

ItemNode() {

this.key = -1;

this.val = -1;

this.freq = -1;

}

}

class FreqNode extends Node {

FreqNode next;

FreqNode prev;

int freq;

ItemNode itemHead;

FreqNode(int freq) {

this.freq = freq;

this.itemHead = newItemHead();

}

FreqNode() {

this.freq = -1;

}

}

abstract class Node {

Node next;

Node prev;

}

}