lru cache: done

Author: rampatra

src/main/java/com/leetcode/design/LFUCache.java

@@ -22,7 +22,7 @@
  * Could you do both operations in O(1) time complexity?
  *
  * Note:
- * -
+ * - When setting a key which is already present, reset its frequency/count to 1.
  *
  * @author rampatra
  * @since 2019-08-20

src/main/java/com/leetcode/design/LRUCache.java

@@ -0,0 +1,61 @@
+package com.leetcode.design;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Level: Medium
+ * Link: https://leetcode.com/problems/lru-cache/
+ * Description:
+ * Design and implement a data structure for Least Recently Used (LRU) cache. 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.
+ *
+ * The cache is initialized with a positive capacity.
+ *
+ * Follow up:
+ * Could you do both operations in O(1) time complexity?
+ *
+ * Runtime: <a href="https://leetcode.com/submissions/detail/253383205/">54 ms</a>.
+ *
+ * @author rampatra
+ * @since 2019-08-20
+ */
+public class LRUCache {
+
+    private LinkedHashMap<Integer, Integer> cache;
+
+    public LRUCache(int capacity) {
+        this.cache = new LinkedHashMap<Integer, Integer>(capacity, 0.75f, true) {
+            @Override
+            protected boolean removeEldestEntry(Map.Entry eldest) {
+                return size() > capacity;
+            }
+        };
+    }
+
+    public int get(int key) {
+        Integer val = cache.get(key);
+        return val == null ? -1 : val;
+    }
+
+    public void put(int key, int value) {
+        cache.put(key, value);
+    }
+
+    public static void main(String[] args) {
+        LRUCache cache = new LRUCache(2);
+        cache.put(1,1);
+        cache.put(2,2);
+        cache.put(1,1);
+        cache.put(3,3);
+        assertEquals(1, cache.get(1));
+        assertEquals(-1, cache.get(2));
+        assertEquals(3, cache.get(3));
+    }
+}