Add LFU Cache (#3161)

src/test/java/com/thealgorithms/datastructures/caches/LFUCacheTest.java

@@ -0,0 +1,67 @@
+package com.thealgorithms.datastructures.caches;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class LFUCacheTest {
+
+	@Test
+	void testLFUCacheWithIntegerValueShouldPass() {
+
+		LFUCache<Integer, Integer> lfuCache = new LFUCache<>(5);
+		lfuCache.put(1, 10);
+		lfuCache.put(2, 20);
+		lfuCache.put(3, 30);
+		lfuCache.put(4, 40);
+		lfuCache.put(5, 50);
+
+		//get method call will increase frequency of key 1 by 1
+		assertEquals(10, lfuCache.get(1));
+
+		//this operation will remove value with key as 2
+		lfuCache.put(6, 60);
+
+		//will return null as value with key 2 is now evicted
+		assertEquals(null, lfuCache.get(2));
+
+		//should return 60
+		assertEquals(60, lfuCache.get(6));
+
+		//this operation will remove value with key as 3
+		lfuCache.put(7, 70);
+
+		assertEquals(null, lfuCache.get(2));
+		assertEquals(70, lfuCache.get(7));
+	}
+
+	@Test
+	void testLFUCacheWithStringValueShouldPass() {
+
+		LFUCache<Integer, String> lfuCache = new LFUCache<>(5);
+		lfuCache.put(1, "Alpha");
+		lfuCache.put(2, "Beta");
+		lfuCache.put(3, "Gamma");
+		lfuCache.put(4, "Delta");
+		lfuCache.put(5, "Eplison");
+
+		//get method call will increase frequency of key 1 by 1
+		assertEquals("Alpha", lfuCache.get(1));
+
+		//this operation will remove value with key as 2
+		lfuCache.put(6, "Digamma");
+
+		//will return null as value with key 2 is now evicted
+		assertEquals(null, lfuCache.get(2));
+
+		//should return string Digamma
+		assertEquals("Digamma", lfuCache.get(6));
+
+		//this operation will remove value with key as 3
+		lfuCache.put(7, "Zeta");
+
+		assertEquals(null, lfuCache.get(2));
+		assertEquals("Zeta", lfuCache.get(7));
+	}
+
+}