BAEL-1010 HLL article code (#2188)

* BAEL-1010 HLL article code

* BAEL-1010 moved tolerated difference to a variable

* Merge branch 'master' of https://github.com/eugenp/tutorials into BAEL-1010_hll

# Conflicts:
#	libraries/pom.xml

libraries/pom.xml

@@ -519,6 +519,11 @@
             <type>jar</type>
         </dependency>
         <!-- /Vaadin -->
+        <dependency>
+            <groupId>net.agkn</groupId>
+            <artifactId>hll</artifactId>
+            <version>${hll.version}</version>
+        </dependency>
     </dependencies>
     <properties>
         <multiverse.version>0.7.0</multiverse.version>
@@ -559,6 +564,7 @@
         <vaadin.plugin.version>8.0.6</vaadin.plugin.version>
         <vaadin.theme>mytheme</vaadin.theme>
         <!-- /Vaadin -->
+        <hll.version>1.6.0</hll.version>
     </properties>
     <profiles>
         <!-- Vaadin -->

libraries/src/test/java/com/baeldung/hll/HLLUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.hll;
+
+
+import com.google.common.hash.HashFunction;
+import com.google.common.hash.Hashing;
+import net.agkn.hll.HLL;
+import org.junit.Test;
+
+import java.util.stream.LongStream;
+
+import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;
+
+public class HLLUnitTest {
+
+    @Test
+    public void givenHLL_whenAddHugeAmountOfNumbers_thenShouldReturnEstimatedCardinality() {
+        //given
+        int numberOfElements = 100_000_000;
+        int toleratedDifference = 1_000_000;
+        HashFunction hashFunction = Hashing.murmur3_128();
+        HLL hll = new HLL(14, 5);
+
+        //when
+        LongStream.range(0, numberOfElements).forEach(element -> {
+                    long hashedValue = hashFunction.newHasher().putLong(element).hash().asLong();
+                    hll.addRaw(hashedValue);
+                }
+        );
+
+        //then
+        long cardinality = hll.cardinality();
+        assertThat(isSimilarTo(cardinality, numberOfElements, toleratedDifference)).isTrue();
+    }
+
+    @Test
+    public void givenTwoHLLs_whenAddHugeAmountOfNumbers_thenShouldReturnEstimatedCardinalityForUnionOfHLLs() {
+        //given
+        int numberOfElements = 100_000_000;
+        int toleratedDifference = 1_000_000;
+        HashFunction hashFunction = Hashing.murmur3_128();
+        HLL firstHll = new HLL(15, 5);
+        HLL secondHLL = new HLL(15, 5);
+
+        //when
+        LongStream.range(0, numberOfElements).forEach(element -> {
+                    long hashedValue = hashFunction.newHasher().putLong(element).hash().asLong();
+                    firstHll.addRaw(hashedValue);
+                }
+        );
+
+        LongStream.range(numberOfElements, numberOfElements * 2).forEach(element -> {
+                    long hashedValue = hashFunction.newHasher().putLong(element).hash().asLong();
+                    secondHLL.addRaw(hashedValue);
+                }
+        );
+
+        //then
+        firstHll.union(secondHLL);
+        long cardinality = firstHll.cardinality();
+        assertThat(isSimilarTo(cardinality, numberOfElements * 2, toleratedDifference)).isTrue();
+    }
+
+    private boolean isSimilarTo(long cardinality, int numberOfElements, int maxToleratedDifference) {
+        System.out.println(cardinality);
+        return Math.abs(cardinality - numberOfElements) <= maxToleratedDifference;
+    }
+}