Add 146_LRU_Cache.java

Author: Sean Prashad

Design/146_LRU_Cache.java

@@ -0,0 +1,82 @@
+class LRUCache {
+ private class Node {
+ private int key, value;
+ private Node next, prev;
+
+ public Node() {
+ key = 0;
+ value = 0;
+ }
+
+ public Node(int k, int v) {
+ key = k;
+ value = v;
+ }
+ }
+
+ private int capacity, currSize;
+ private Node head, tail;
+ private Map<Integer, Node> map;
+
+ public LRUCache(int capacity) {
+ this.capacity = capacity;
+ currSize = 0;
+ map = new HashMap<>();
+ head = new Node();
+ tail = new Node();
+ head.next = tail;
+ tail.prev = head;
+ }
+
+ public int get(int key) {
+ if (!map.containsKey(key)) {
+ return -1;
+ }
+
+ Node n = map.get(key);
+ update(n);
+ return n.value;
+ }
+
+ public void put(int key, int value) {
+ Node n = map.get(key);
+
+ if (n == null) {
+ n = new Node(key, value);
+ map.put(key, n);
+ add(n);
+ ++currSize;
+ } else {
+ n.value = value;
+ map.put(key, n);
+ update(n);
+ }
+
+ if (currSize > capacity) {
+ Node toDelete = tail.prev;
+ remove(toDelete);
+ map.remove(toDelete.key);
+ --currSize;
+ }
+ }
+
+ private void update(Node n) {
+ remove(n);
+ add(n);
+ }
+
+ private void remove(Node n) {
+ Node before = n.prev, after = n.next;
+ before.next = after;
+ after.prev = before;
+ }
+
+ private void add(Node n) {
+ Node after = head.next;
+
+ head.next = n;
+ n.prev = head;
+ n.next = after;
+ after.prev = n;
+ }
+}