added solution to implement LRU cache

YogenRaii · YogenRaii · commit a38edee20e65 · 2019-06-23T16:44:42.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/PowerSet.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/PowerSet.java
@@ -36,8 +36,7 @@ public static Set<Set<Integer>> getSubsets(List<Integer> integers, int index) {
             Integer item = integers.get(index);
             Set<Set<Integer>> moreSubset = new LinkedHashSet<>();
             for (Set<Integer> subset: powerSet) {
-                Set<Integer> newSubset = new LinkedHashSet<>();
-                newSubset.addAll(subset);
+                Set<Integer> newSubset = new LinkedHashSet<>(subset);
                 newSubset.add(item);
                 moreSubset.add(newSubset);
             }
diff --git a/src/main/java/com/eprogrammerz/examples/ds/cache/LRUCache.java b/src/main/java/com/eprogrammerz/examples/ds/cache/LRUCache.java
@@ -0,0 +1,111 @@
+package com.eprogrammerz.examples.ds.cache;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.PriorityQueue;
+
+/**
+ * Design LRU cache with fix size i.e. if cache reaches max size, then least recently has to be removed!
+ *
+ * 2 -> (2,yogen,next,prev)
+ * 3 -> (3,rai,next,prev)
+ * 4 -> (4,nepal,next,prev)
+ * 1 -> (1,intro)
+ *
+ *
+ * head will track to MRU and tail will track to LRU
+ *
+ * 2,yogen -> 3,rai -> 4,nepal
+ * cache.get(3)
+ * 3,rai -> 2,yogen -> 4,nepal
+ * cache.put(1)
+ * 1,intro -> 2,yogen -> 4,nepal
+ *
+ */
+public class LRUCache<K, V> {
+
+    private class Node<K,V> {
+        K key;
+        V value;
+
+        Node<K,V> next;
+        Node<K,V> prev;
+
+        Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
+
+        @Override
+        public String toString() {
+            return "(" + key + ", " + value + ")";
+        }
+    }
+
+    private int size;
+
+    private Map<K,Node<K,V>> map;
+
+    private Node<K, V> head;
+    private Node<K, V> tail;
+
+    public LRUCache(int initialCapacity) {
+        this.size = initialCapacity;
+        this.map = new HashMap<>(initialCapacity);
+    }
+
+    public void put(K key, V value) {
+        Node<K,V> node = new Node<>(key, value);
+        if (size == map.size()) {
+            // remove tail
+            map.remove(tail.key);
+            removeNode(tail);
+
+        }
+        insertNodeAtFirst(node);
+
+        map.put(key, node);
+    }
+
+    private void insertNodeAtFirst(Node<K, V> node) {
+        if (head == null) {
+            head = node;
+            tail = node;
+        } else {
+            node.next = head;
+            head.prev = node;
+            head = node;
+        }
+    }
+
+    public V get(K key) {
+        Node<K,V> node = map.get(key);
+
+        if (node == null) return null;
+
+        if (node != head) {
+            // remove node from its current spot
+            removeNode(node);
+
+            // add to the from of the list
+            insertNodeAtFirst(node);
+        }
+
+        return node.value;
+    }
+
+    private void removeNode(Node<K, V> node) {
+        if (node == null) return;
+
+        if (node.prev != null) {
+            node.prev.next = node.next;
+        }
+
+        if (node.next != null) {
+            node.next.prev = node.prev;
+        }
+        if (tail == node) tail = node.prev;
+        if (head == node) head = node.next;
+    }
+
+}
diff --git a/src/main/java/com/eprogrammerz/examples/ds/cache/LRUCacheTest.java b/src/main/java/com/eprogrammerz/examples/ds/cache/LRUCacheTest.java
@@ -0,0 +1,27 @@
+package com.eprogrammerz.examples.ds.cache;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+public class LRUCacheTest {
+    @Test
+    public void testLRUCache() {
+        LRUCache<String, String> cache = new LRUCache<>(3);
+        cache.put("Yogen", "rai1");
+        cache.put("Pratima", "rai2");
+        cache.put("Yogesh", "rai3");
+
+        assertEquals("rai1", (cache.get("Yogen"))); // ["Yogesh", "Pratima", "Yogen"]
+        assertEquals("rai2", cache.get("Pratima")); // ["Pratima", "Yogesh", "Yogen"]
+
+        cache.put("Srijana", "khaling");
+        cache.put("another", "another");
+        assertNull(cache.get("Yogen"));
+        assertNull(cache.get("Yogesh"));
+        assertEquals("rai2", cache.get("Pratima"));
+        assertEquals("khaling", cache.get("Srijana"));
+        assertEquals("another", cache.get("another")); // ["another", "srijana", "Pratima"]
+    }
+}
