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/**

* 146. LRU Cache

*

* Design and implement a data structure for Least Recently Used (LRU) cache.

* https://en.wikipedia.org/wiki/Cache_replacement_policies#LRU

*

* It should support the following operations: get and put.

*

* get(key) - Get the value (will always be positive) of the key if the key

* exists in the cache, otherwise return -1.

* put(key, value) - Set or insert the value if the key is not already present.

* When the cache reached its capacity, it should invalidate

* the least recently used item before inserting a new item.

*

* Follow up:

* Could you do both operations in O(1) time complexity?

*

* Example:

*

* LRUCache cache = new LRUCache( 2 ); // capacity

*

* 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

*/

/**

* Your LRUCache object will be instantiated and called as such:

* LRUCache obj = new LRUCache(capacity);

* int param_1 = obj.get(key);

* obj.put(key,value);

*/

import java.util.LinkedHashMap;

import java.util.Map;

public class LRUCache {

private Map<Integer, Node> map = new HashMap<>();

private Node head = new Node(0, 0);

private int capacity;

public LRUCache(int capacity) {

head.next = head;

head.prev = head;

this.capacity = capacity;

}

public int get(int key) {

Node curr = map.get(key);

if (curr == null) {

return -1;

}

delete(curr);

moveToEnd(curr);

return curr.value;

}

private void delete(Node node) {

node.prev.next = node.next;

node.next.prev = node.prev;

}

private void moveToEnd(Node node) {

head.prev.next = node;

node.next = head;

node.prev = head.prev;

head.prev = node;

}

public void put(int key, int value) {

Node curr = map.get(key);

if (curr == null) {

Node newNode = new Node(key, value);

moveToEnd(newNode);

map.put(key, newNode);

if (map.size() > capacity) {

Node toRemove = head.next;

delete(toRemove);

map.remove(toRemove.key);

}

return;

}

curr.value = value;

delete(curr);

moveToEnd(curr);

}

class Node {

int key;

int value;

Node next;

Node prev;

Node (int k, int v) {

this.key = k;

this.value = v;

}

}

}