Merge branch 'master' into master

2019-09-14 18:33:59 +02:00
parent 7da248c9db c291aae952
commit eafae99b79
1623 changed files with 248849 additions and 8250 deletions
@@ -1,24 +0,0 @@
-language: java
-
-before_install: 
-  - echo "MAVEN_OPTS='-Xmx2048M -Xss128M -XX:+CMSClassUnloadingEnabled -XX:+UseG1GC -XX:-UseGCOverheadLimit'" > ~/.mavenrc
-
-install: skip
-script: travis_wait 60 mvn -q install -Pdefault-first,default-second -Dgib.enabled=true
-
-sudo: required
-
-jdk:
-  - oraclejdk8
-
-addons:
-  apt:
-    packages:
-      - oracle-java8-installer
-
-cache:
-  directories:
-  - .autoconf
-  - $HOME/.m2
-  
-
@@ -7,3 +7,4 @@
 - [Checking If a List Is Sorted in Java](https://www.baeldung.com/java-check-if-list-sorted)
 - [Checking if a Java Graph has a Cycle](https://www.baeldung.com/java-graph-has-a-cycle)
 - [A Guide to the Folding Technique in Java](https://www.baeldung.com/folding-hashing-technique)
+- [Creating a Triangle with for Loops in Java](https://www.baeldung.com/java-print-triangle)
@@ -1,5 +1,5 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <artifactId>algorithms-miscellaneous-3</artifactId>
    <version>0.0.1-SNAPSHOT</version>
@@ -18,17 +18,28 @@
            <version>${org.assertj.core.version}</version>
            <scope>test</scope>
        </dependency>
-        
+
        <dependency>
-        	<groupId>org.apache.commons</groupId>
-        	<artifactId>commons-collections4</artifactId>
-        	<version>${commons-collections4.version}</version>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
        </dependency>
-        
+
        <dependency>
-        	<groupId>com.google.guava</groupId>
-        	<artifactId>guava</artifactId>
-        	<version>${guava.version}</version>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>retrofit</artifactId>
+            <version>${retrofit.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>converter-jackson</artifactId>
+            <version>${retrofit.version}</version>
        </dependency>

        <dependency>
@@ -61,5 +72,6 @@
        <org.assertj.core.version>3.9.0</org.assertj.core.version>
        <commons-collections4.version>4.3</commons-collections4.version>
        <guava.version>28.0-jre</guava.version>
+        <retrofit.version>2.6.0</retrofit.version>
    </properties>
 </project>
@@ -0,0 +1,70 @@
+package com.baeldung.bucketsort;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+public class IntegerBucketSorter implements Sorter<Integer> {
+
+    private final Comparator<Integer> comparator;
+
+    public IntegerBucketSorter(Comparator<Integer> comparator) {
+        this.comparator = comparator;
+    }
+
+    public IntegerBucketSorter() {
+        comparator = Comparator.naturalOrder();
+    }
+
+    public List<Integer> sort(List<Integer> arrayToSort) {
+
+        List<List<Integer>> buckets = splitIntoUnsortedBuckets(arrayToSort);
+
+        for(List<Integer> bucket  : buckets){
+            bucket.sort(comparator);
+        }
+
+        return concatenateSortedBuckets(buckets);
+    }
+
+    private List<Integer> concatenateSortedBuckets(List<List<Integer>> buckets){
+        List<Integer> sortedArray = new ArrayList<>();
+        int index = 0;
+        for(List<Integer> bucket : buckets){
+            for(int number : bucket){
+                sortedArray.add(index++, number);
+            }
+        }
+        return sortedArray;
+    }
+
+    private List<List<Integer>> splitIntoUnsortedBuckets(List<Integer> initialList){
+
+        final int[] codes = createHashes(initialList);
+
+        List<List<Integer>> buckets = new ArrayList<>(codes[1]);
+        for(int i = 0; i < codes[1]; i++) buckets.add(new ArrayList<>());
+
+        //distribute the data
+        for (int i : initialList) {
+            buckets.get(hash(i, codes)).add(i);
+        }
+        return buckets;
+
+    }
+
+    private int[] createHashes(List<Integer> input){
+        int m = input.get(0);
+        for (int i = 1; i < input.size(); i++) {
+            if (m < input.get(i)) {
+                m = input.get(i);
+            }
+        }
+        return new int[]{m, (int) Math.sqrt(input.size())};
+    }
+
+    private static int hash(int i, int[] code) {
+        return (int) ((double) i / code[0] * (code[1] - 1));
+    }
+
+}
@@ -0,0 +1,8 @@
+package com.baeldung.bucketsort;
+
+import java.util.List;
+
+public interface Sorter<T> {
+
+    List<T> sort(List<T> arrayToSort);
+}
@@ -0,0 +1,35 @@
+package com.baeldung.algorithms.interpolationsearch;
+
+public class InterpolationSearch {
+
+    public static int interpolationSearch(int[] data, int item) {
+
+        int highEnd = (data.length - 1);
+        int lowEnd = 0;
+
+        while (item >= data[lowEnd] && item <= data[highEnd] && lowEnd <= highEnd) {
+
+            int probe = lowEnd + (highEnd - lowEnd) * (item - data[lowEnd]) / (data[highEnd] - data[lowEnd]);
+
+            if (highEnd == lowEnd) {
+                if (data[lowEnd] == item) {
+                    return lowEnd;
+                } else {
+                    return -1;
+                }
+            }
+
+            if (data[probe] == item) {
+                return probe;
+            }
+
+            if (data[probe] < item) {
+                lowEnd = probe + 1;
+            } else {
+                highEnd = probe - 1;
+            }
+        }
+        return -1;
+    }
+
+}
@@ -0,0 +1,45 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Encapsulates all coordinates for a particular cluster centroid.
+ */
+public class Centroid {
+
+    /**
+     * The centroid coordinates.
+     */
+    private final Map<String, Double> coordinates;
+
+    public Centroid(Map<String, Double> coordinates) {
+        this.coordinates = coordinates;
+    }
+
+    public Map<String, Double> getCoordinates() {
+        return coordinates;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Centroid centroid = (Centroid) o;
+        return Objects.equals(getCoordinates(), centroid.getCoordinates());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getCoordinates());
+    }
+
+    @Override
+    public String toString() {
+        return "Centroid " + coordinates;
+    }
+}
@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+
+/**
+ * Defines a contract to calculate distance between two feature vectors. The less the
+ * calculated distance, the more two items are similar to each other.
+ */
+public interface Distance {
+
+    /**
+     * Calculates the distance between two feature vectors.
+     *
+     * @param f1 The first set of features.
+     * @param f2 The second set of features.
+     * @return Calculated distance.
+     * @throws IllegalArgumentException If the given feature vectors are invalid.
+     */
+    double calculate(Map<String, Double> f1, Map<String, Double> f2);
+}
@@ -0,0 +1,23 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Encapsulates methods to calculates errors between centroid and the cluster members.
+ */
+public class Errors {
+
+    public static double sse(Map<Centroid, List<Record>> clustered, Distance distance) {
+        double sum = 0;
+        for (Map.Entry<Centroid, List<Record>> entry : clustered.entrySet()) {
+            Centroid centroid = entry.getKey();
+            for (Record record : entry.getValue()) {
+                double d = distance.calculate(centroid.getCoordinates(), record.getFeatures());
+                sum += Math.pow(d, 2);
+            }
+        }
+
+        return sum;
+    }
+}
@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+
+/**
+ * Calculates the distance between two items using the Euclidean formula.
+ */
+public class EuclideanDistance implements Distance {
+
+    @Override
+    public double calculate(Map<String, Double> f1, Map<String, Double> f2) {
+        if (f1 == null || f2 == null) {
+            throw new IllegalArgumentException("Feature vectors can't be null");
+        }
+
+        double sum = 0;
+        for (String key : f1.keySet()) {
+            Double v1 = f1.get(key);
+            Double v2 = f2.get(key);
+
+            if (v1 != null && v2 != null) sum += Math.pow(v1 - v2, 2);
+        }
+
+        return Math.sqrt(sum);
+    }
+}
@@ -0,0 +1,236 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.Set;
+
+import static java.util.stream.Collectors.toList;
+import static java.util.stream.Collectors.toSet;
+
+/**
+ * Encapsulates an implementation of KMeans clustering algorithm.
+ *
+ * @author Ali Dehghani
+ */
+public class KMeans {
+
+    private KMeans() {
+        throw new IllegalAccessError("You shouldn't call this constructor");
+    }
+
+    /**
+     * Will be used to generate random numbers.
+     */
+    private static final Random random = new Random();
+
+    /**
+     * Performs the K-Means clustering algorithm on the given dataset.
+     *
+     * @param records       The dataset.
+     * @param k             Number of Clusters.
+     * @param distance      To calculate the distance between two items.
+     * @param maxIterations Upper bound for the number of iterations.
+     * @return K clusters along with their features.
+     */
+    public static Map<Centroid, List<Record>> fit(List<Record> records, int k, Distance distance, int maxIterations) {
+        applyPreconditions(records, k, distance, maxIterations);
+
+        List<Centroid> centroids = randomCentroids(records, k);
+        Map<Centroid, List<Record>> clusters = new HashMap<>();
+        Map<Centroid, List<Record>> lastState = new HashMap<>();
+
+        // iterate for a pre-defined number of times
+        for (int i = 0; i < maxIterations; i++) {
+            boolean isLastIteration = i == maxIterations - 1;
+
+            // in each iteration we should find the nearest centroid for each record
+            for (Record record : records) {
+                Centroid centroid = nearestCentroid(record, centroids, distance);
+                assignToCluster(clusters, record, centroid);
+            }
+
+            // if the assignment does not change, then the algorithm terminates
+            boolean shouldTerminate = isLastIteration || clusters.equals(lastState);
+            lastState = clusters;
+            if (shouldTerminate) {
+                break;
+            }
+
+            // at the end of each iteration we should relocate the centroids
+            centroids = relocateCentroids(clusters);
+            clusters = new HashMap<>();
+        }
+
+        return lastState;
+    }
+
+    /**
+     * Move all cluster centroids to the average of all assigned features.
+     *
+     * @param clusters The current cluster configuration.
+     * @return Collection of new and relocated centroids.
+     */
+    private static List<Centroid> relocateCentroids(Map<Centroid, List<Record>> clusters) {
+        return clusters
+          .entrySet()
+          .stream()
+          .map(e -> average(e.getKey(), e.getValue()))
+          .collect(toList());
+    }
+
+    /**
+     * Moves the given centroid to the average position of all assigned features. If
+     * the centroid has no feature in its cluster, then there would be no need for a
+     * relocation. Otherwise, for each entry we calculate the average of all records
+     * first by summing all the entries and then dividing the final summation value by
+     * the number of records.
+     *
+     * @param centroid The centroid to move.
+     * @param records  The assigned features.
+     * @return The moved centroid.
+     */
+    private static Centroid average(Centroid centroid, List<Record> records) {
+        // if this cluster is empty, then we shouldn't move the centroid
+        if (records == null || records.isEmpty()) {
+            return centroid;
+        }
+
+        // Since some records don't have all possible attributes, we initialize
+        // average coordinates equal to current centroid coordinates
+        Map<String, Double> average = centroid.getCoordinates();
+
+        // The average function works correctly if we clear all coordinates corresponding
+        // to present record attributes
+        records
+          .stream()
+          .flatMap(e -> e
+            .getFeatures()
+            .keySet()
+            .stream())
+          .forEach(k -> average.put(k, 0.0));
+
+        for (Record record : records) {
+            record
+              .getFeatures()
+              .forEach((k, v) -> average.compute(k, (k1, currentValue) -> v + currentValue));
+        }
+
+        average.forEach((k, v) -> average.put(k, v / records.size()));
+
+        return new Centroid(average);
+    }
+
+    /**
+     * Assigns a feature vector to the given centroid. If this is the first assignment for this centroid,
+     * first we should create the list.
+     *
+     * @param clusters The current cluster configuration.
+     * @param record   The feature vector.
+     * @param centroid The centroid.
+     */
+    private static void assignToCluster(Map<Centroid, List<Record>> clusters, Record record, Centroid centroid) {
+        clusters.compute(centroid, (key, list) -> {
+            if (list == null) {
+                list = new ArrayList<>();
+            }
+
+            list.add(record);
+            return list;
+        });
+    }
+
+    /**
+     * With the help of the given distance calculator, iterates through centroids and finds the
+     * nearest one to the given record.
+     *
+     * @param record    The feature vector to find a centroid for.
+     * @param centroids Collection of all centroids.
+     * @param distance  To calculate the distance between two items.
+     * @return The nearest centroid to the given feature vector.
+     */
+    private static Centroid nearestCentroid(Record record, List<Centroid> centroids, Distance distance) {
+        double minimumDistance = Double.MAX_VALUE;
+        Centroid nearest = null;
+
+        for (Centroid centroid : centroids) {
+            double currentDistance = distance.calculate(record.getFeatures(), centroid.getCoordinates());
+
+            if (currentDistance < minimumDistance) {
+                minimumDistance = currentDistance;
+                nearest = centroid;
+            }
+        }
+
+        return nearest;
+    }
+
+    /**
+     * Generates k random centroids. Before kicking-off the centroid generation process,
+     * first we calculate the possible value range for each attribute. Then when
+     * we're going to generate the centroids, we generate random coordinates in
+     * the [min, max] range for each attribute.
+     *
+     * @param records The dataset which helps to calculate the [min, max] range for
+     *                each attribute.
+     * @param k       Number of clusters.
+     * @return Collections of randomly generated centroids.
+     */
+    private static List<Centroid> randomCentroids(List<Record> records, int k) {
+        List<Centroid> centroids = new ArrayList<>();
+        Map<String, Double> maxs = new HashMap<>();
+        Map<String, Double> mins = new HashMap<>();
+
+        for (Record record : records) {
+            record
+              .getFeatures()
+              .forEach((key, value) -> {
+                  // compares the value with the current max and choose the bigger value between them
+                  maxs.compute(key, (k1, max) -> max == null || value > max ? value : max);
+
+                  // compare the value with the current min and choose the smaller value between them
+                  mins.compute(key, (k1, min) -> min == null || value < min ? value : min);
+              });
+        }
+
+        Set<String> attributes = records
+          .stream()
+          .flatMap(e -> e
+            .getFeatures()
+            .keySet()
+            .stream())
+          .collect(toSet());
+        for (int i = 0; i < k; i++) {
+            Map<String, Double> coordinates = new HashMap<>();
+            for (String attribute : attributes) {
+                double max = maxs.get(attribute);
+                double min = mins.get(attribute);
+                coordinates.put(attribute, random.nextDouble() * (max - min) + min);
+            }
+
+            centroids.add(new Centroid(coordinates));
+        }
+
+        return centroids;
+    }
+
+    private static void applyPreconditions(List<Record> records, int k, Distance distance, int maxIterations) {
+        if (records == null || records.isEmpty()) {
+            throw new IllegalArgumentException("The dataset can't be empty");
+        }
+
+        if (k <= 1) {
+            throw new IllegalArgumentException("It doesn't make sense to have less than or equal to 1 cluster");
+        }
+
+        if (distance == null) {
+            throw new IllegalArgumentException("The distance calculator is required");
+        }
+
+        if (maxIterations <= 0) {
+            throw new IllegalArgumentException("Max iterations should be a positive number");
+        }
+    }
+}
@@ -0,0 +1,144 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import okhttp3.OkHttpClient;
+import retrofit2.Retrofit;
+import retrofit2.converter.jackson.JacksonConverterFactory;
+
+import static java.util.stream.Collectors.toSet;
+
+public class LastFm {
+
+    private static OkHttpClient okHttp = new OkHttpClient.Builder()
+      .addInterceptor(new LastFmService.Authenticator("put your API key here"))
+      .build();
+
+    private static Retrofit retrofit = new Retrofit.Builder()
+      .client(okHttp)
+      .addConverterFactory(JacksonConverterFactory.create())
+      .baseUrl("http://ws.audioscrobbler.com/")
+      .build();
+
+    private static LastFmService lastFm = retrofit.create(LastFmService.class);
+
+    private static ObjectMapper mapper = new ObjectMapper();
+
+    public static void main(String[] args) throws IOException {
+        List<String> artists = getTop100Artists();
+        Set<String> tags = getTop100Tags();
+        List<Record> records = datasetWithTaggedArtists(artists, tags);
+
+        Map<Centroid, List<Record>> clusters = KMeans.fit(records, 7, new EuclideanDistance(), 1000);
+        // Print the cluster configuration
+        clusters.forEach((key, value) -> {
+            System.out.println("------------------------------ CLUSTER -----------------------------------");
+
+            System.out.println(sortedCentroid(key));
+            String members = String.join(", ", value
+              .stream()
+              .map(Record::getDescription)
+              .collect(toSet()));
+            System.out.print(members);
+
+            System.out.println();
+            System.out.println();
+        });
+
+        Map<String, Object> json = convertToD3CompatibleMap(clusters);
+        System.out.println(mapper.writeValueAsString(json));
+    }
+
+    private static Map<String, Object> convertToD3CompatibleMap(Map<Centroid, List<Record>> clusters) {
+        Map<String, Object> json = new HashMap<>();
+        json.put("name", "Musicians");
+        List<Map<String, Object>> children = new ArrayList<>();
+        clusters.forEach((key, value) -> {
+            Map<String, Object> child = new HashMap<>();
+            child.put("name", dominantGenre(sortedCentroid(key)));
+            List<Map<String, String>> nested = new ArrayList<>();
+            for (Record record : value) {
+                nested.add(Collections.singletonMap("name", record.getDescription()));
+            }
+            child.put("children", nested);
+
+            children.add(child);
+        });
+        json.put("children", children);
+        return json;
+    }
+
+    private static String dominantGenre(Centroid centroid) {
+        return centroid
+          .getCoordinates()
+          .keySet()
+          .stream()
+          .limit(2)
+          .collect(Collectors.joining(", "));
+    }
+
+    private static Centroid sortedCentroid(Centroid key) {
+        List<Map.Entry<String, Double>> entries = new ArrayList<>(key
+          .getCoordinates()
+          .entrySet());
+        entries.sort((e1, e2) -> e2
+          .getValue()
+          .compareTo(e1.getValue()));
+
+        Map<String, Double> sorted = new LinkedHashMap<>();
+        for (Map.Entry<String, Double> entry : entries) {
+            sorted.put(entry.getKey(), entry.getValue());
+        }
+
+        return new Centroid(sorted);
+    }
+
+    private static List<Record> datasetWithTaggedArtists(List<String> artists, Set<String> topTags) throws IOException {
+        List<Record> records = new ArrayList<>();
+        for (String artist : artists) {
+            Map<String, Double> tags = lastFm
+              .topTagsFor(artist)
+              .execute()
+              .body()
+              .all();
+
+            // Only keep popular tags.
+            tags
+              .entrySet()
+              .removeIf(e -> !topTags.contains(e.getKey()));
+
+            records.add(new Record(artist, tags));
+        }
+        return records;
+    }
+
+    private static Set<String> getTop100Tags() throws IOException {
+        return lastFm
+          .topTags()
+          .execute()
+          .body()
+          .all();
+    }
+
+    private static List<String> getTop100Artists() throws IOException {
+        List<String> artists = new ArrayList<>();
+        for (int i = 1; i <= 2; i++) {
+            artists.addAll(lastFm
+              .topArtists(i)
+              .execute()
+              .body()
+              .all());
+        }
+
+        return artists;
+    }
+}
@@ -0,0 +1,118 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import okhttp3.HttpUrl;
+import okhttp3.Interceptor;
+import okhttp3.Request;
+import okhttp3.Response;
+import retrofit2.Call;
+import retrofit2.http.GET;
+import retrofit2.http.Query;
+
+import static com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.ANY;
+import static java.util.stream.Collectors.toList;
+
+public interface LastFmService {
+
+    @GET("/2.0/?method=chart.gettopartists&format=json&limit=50")
+    Call<Artists> topArtists(@Query("page") int page);
+
+    @GET("/2.0/?method=artist.gettoptags&format=json&limit=20&autocorrect=1")
+    Call<Tags> topTagsFor(@Query("artist") String artist);
+
+    @GET("/2.0/?method=chart.gettoptags&format=json&limit=100")
+    Call<TopTags> topTags();
+
+    /**
+     * HTTP interceptor to intercept all HTTP requests and add the API key to them.
+     */
+    class Authenticator implements Interceptor {
+
+        private final String apiKey;
+
+        Authenticator(String apiKey) {
+            this.apiKey = apiKey;
+        }
+
+        @Override
+        public Response intercept(Chain chain) throws IOException {
+            HttpUrl url = chain
+              .request()
+              .url()
+              .newBuilder()
+              .addQueryParameter("api_key", apiKey)
+              .build();
+            Request request = chain
+              .request()
+              .newBuilder()
+              .url(url)
+              .build();
+
+            return chain.proceed(request);
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class TopTags {
+
+        private Map<String, Object> tags;
+
+        @SuppressWarnings("unchecked")
+        public Set<String> all() {
+            List<Map<String, Object>> topTags = (List<Map<String, Object>>) tags.get("tag");
+            return topTags
+              .stream()
+              .map(e -> ((String) e.get("name")))
+              .collect(Collectors.toSet());
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class Tags {
+
+        @JsonProperty("toptags") private Map<String, Object> topTags;
+
+        @SuppressWarnings("unchecked")
+        public Map<String, Double> all() {
+            try {
+                Map<String, Double> all = new HashMap<>();
+                List<Map<String, Object>> tags = (List<Map<String, Object>>) topTags.get("tag");
+                for (Map<String, Object> tag : tags) {
+                    all.put(((String) tag.get("name")), ((Integer) tag.get("count")).doubleValue());
+                }
+
+                return all;
+            } catch (Exception e) {
+                return Collections.emptyMap();
+            }
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class Artists {
+
+        private Map<String, Object> artists;
+
+        @SuppressWarnings("unchecked")
+        public List<String> all() {
+            try {
+                List<Map<String, Object>> artists = (List<Map<String, Object>>) this.artists.get("artist");
+                return artists
+                  .stream()
+                  .map(e -> ((String) e.get("name")))
+                  .collect(toList());
+            } catch (Exception e) {
+                return Collections.emptyList();
+            }
+        }
+    }
+}
@@ -0,0 +1,65 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Encapsulates all feature values for a few attributes. Optionally each record
+ * can be described with the {@link #description} field.
+ */
+public class Record {
+
+    /**
+     * The record description. For example, this can be the artist name for the famous musician
+     * example.
+     */
+    private final String description;
+
+    /**
+     * Encapsulates all attributes and their corresponding values, i.e. features.
+     */
+    private final Map<String, Double> features;
+
+    public Record(String description, Map<String, Double> features) {
+        this.description = description;
+        this.features = features;
+    }
+
+    public Record(Map<String, Double> features) {
+        this("", features);
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public Map<String, Double> getFeatures() {
+        return features;
+    }
+
+    @Override
+    public String toString() {
+        String prefix = description == null || description
+          .trim()
+          .isEmpty() ? "Record" : description;
+
+        return prefix + ": " + features;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Record record = (Record) o;
+        return Objects.equals(getDescription(), record.getDescription()) && Objects.equals(getFeatures(), record.getFeatures());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getDescription(), getFeatures());
+    }
+}
@@ -4,7 +4,7 @@ import org.apache.commons.lang3.StringUtils;

 public class PrintTriangleExamples {

-    public static String printARightAngledTriangle(int N) {
+    public static String printARightTriangle(int N) {
        StringBuilder result = new StringBuilder();
        for (int r = 1; r <= N; r++) {
            for (int j = 1; j <= r; j++) {
@@ -29,6 +29,17 @@ public class PrintTriangleExamples {
        return result.toString();
    }

+    public static String printAnIsoscelesTriangleUsingStringUtils(int N) {
+        StringBuilder result = new StringBuilder();
+
+        for (int r = 1; r <= N; r++) {
+            result.append(StringUtils.repeat(' ', N - r));
+            result.append(StringUtils.repeat('*', 2 * r - 1));
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
    public static String printAnIsoscelesTriangleUsingSubstring(int N) {
        StringBuilder result = new StringBuilder();
        String helperString = StringUtils.repeat(' ', N - 1) + StringUtils.repeat('*', N * 2 - 1);
@@ -41,8 +52,9 @@ public class PrintTriangleExamples {
    }

    public static void main(String[] args) {
-        System.out.println(printARightAngledTriangle(5));
+        System.out.println(printARightTriangle(5));
        System.out.println(printAnIsoscelesTriangle(5));
+        System.out.println(printAnIsoscelesTriangleUsingStringUtils(5));
        System.out.println(printAnIsoscelesTriangleUsingSubstring(5));
    }

@@ -0,0 +1,68 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<style>
+    .node circle {
+        fill: #fff;
+        stroke: steelblue;
+        stroke-width: 1.5px;
+    }
+
+    .node {
+        font: 10px sans-serif;
+    }
+
+    .link {
+        fill: none;
+        stroke: #ccc;
+        stroke-width: 1.5px;
+    }
+</style>
+<body>
+<script src="http://d3js.org/d3.v3.min.js"></script>
+<script>
+    var diameter = 1100;
+    var tree = d3.layout.tree()
+        .size([360, diameter / 2 - 300])
+        .separation(function (a, b) {
+            return (a.parent == b.parent ? 1 : 2) / a.depth;
+        });
+    var diagonal = d3.svg.diagonal.radial()
+        .projection(function (d) {
+            return [d.y, d.x / 180 * Math.PI];
+        });
+    var svg = d3.select("body").append("svg")
+        .attr("width", diameter)
+        .attr("height", diameter - 150)
+        .append("g")
+        .attr("transform", "translate(" + diameter / 2 + "," + diameter / 2 + ")");
+    d3.json("lastfm.json", function (error, root) {
+        var nodes = tree.nodes(root),
+            links = tree.links(nodes);
+        var link = svg.selectAll(".link")
+            .data(links)
+            .enter().append("path")
+            .attr("class", "link")
+            .attr("d", diagonal);
+        var node = svg.selectAll(".node")
+            .data(nodes)
+            .enter().append("g")
+            .attr("class", "node")
+            .attr("transform", function (d) {
+                return "rotate(" + (d.x - 90) + ")translate(" + d.y + ")";
+            })
+        node.append("circle")
+            .attr("r", 4.5);
+        node.append("text")
+            .attr("dy", ".31em")
+            .attr("text-anchor", function (d) {
+                return d.x < 180 ? "start" : "end";
+            })
+            .attr("transform", function (d) {
+                return d.x < 180 ? "translate(8)" : "rotate(180)translate(-8)";
+            })
+            .text(function (d) {
+                return d.name;
+            });
+    });
+    d3.select(self.frameElement).style("height", diameter - 150 + "px");
+</script>
@@ -0,0 +1,33 @@
+package com.baeldung.bucketsort;
+
+import com.baeldung.bucketsort.IntegerBucketSorter;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class IntegerBucketSorterUnitTest {
+
+    private IntegerBucketSorter sorter;
+
+    @Before
+    public void setUp() throws Exception {
+        sorter = new IntegerBucketSorter();
+    }
+
+    @Test
+    public void givenUnsortedList_whenSortedUsingBucketSorter_checkSortingCorrect() {
+
+        List<Integer> unsorted = Arrays.asList(80,50,60,30,20,10,70,0,40,500,600,602,200,15);
+        List<Integer> expected = Arrays.asList(0,10,15,20,30,40,50,60,70,80,200,500,600,602);
+
+        List<Integer> actual = sorter.sort(unsorted);
+
+        assertEquals(expected, actual);
+
+
+    }
+}
@@ -0,0 +1,29 @@
+package com.baeldung.algorithms.interpolationsearch;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class InterpolationSearchUnitTest {
+    
+    private int[] myData;
+
+    @Before
+    public void setUp() {
+        myData = new int[]{13,21,34,55,69,73,84,101};
+    }
+    
+    @Test
+    public void givenSortedArray_whenLookingFor84_thenReturn6() {
+        int pos = InterpolationSearch.interpolationSearch(myData, 84);
+        assertEquals(6, pos);
+    }
+    
+    @Test
+    public void givenSortedArray_whenLookingFor19_thenReturnMinusOne() {
+        int pos = InterpolationSearch.interpolationSearch(myData, 19);
+        assertEquals(-1, pos);
+    }
+
+}
@@ -9,9 +9,9 @@ import static org.junit.Assert.assertEquals;

@RunWith(JUnitParamsRunner.class)
 public class PrintTriangleExamplesUnitTest {
-    
-    private static Object[][] rightAngledTriangles() {
-        String expected0 = ""; 
+
+    private static Object[][] rightTriangles() {
+        String expected0 = "";
        
        String expected2 = "*" + System.lineSeparator() 
                         + "**" + System.lineSeparator();
@@ -39,9 +39,9 @@ public class PrintTriangleExamplesUnitTest {
    }

    @Test
-    @Parameters(method = "rightAngledTriangles")
-    public void whenPrintARightAngledTriangleIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
-        String actual = PrintTriangleExamples.printARightAngledTriangle(nrOfRows);
+    @Parameters(method = "rightTriangles")
+    public void whenPrintARightTriangleIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printARightTriangle(nrOfRows);

        assertEquals(expected, actual);
    }
@@ -81,6 +81,14 @@ public class PrintTriangleExamplesUnitTest {

        assertEquals(expected, actual);
    }
+
+    @Test
+    @Parameters(method = "isoscelesTriangles")
+    public void whenPrintAnIsoscelesTriangleUsingStringUtilsIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printAnIsoscelesTriangleUsingStringUtils(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
    
    @Test
    @Parameters(method = "isoscelesTriangles")
@@ -5,3 +5,5 @@
 - [Quicksort Algorithm Implementation in Java](https://www.baeldung.com/java-quicksort)
 - [Insertion Sort in Java](https://www.baeldung.com/java-insertion-sort)
 - [Heap Sort in Java](https://www.baeldung.com/java-heap-sort)
+- [Shell Sort in Java](https://www.baeldung.com/java-shell-sort)
+- [Counting Sort in Java](https://www.baeldung.com/java-counting-sort)
@@ -0,0 +1,48 @@
+package com.baeldung.algorithms.counting;
+
+import java.util.Arrays;
+import java.util.stream.IntStream;
+
+public class CountingSort {
+
+    public static int[] sort(int[] input, int k) {
+        verifyPreconditions(input, k);
+        if (input.length == 0) return input;
+
+        int[] c = countElements(input, k);
+        int[] sorted = new int[input.length];
+        for (int i = input.length - 1; i >= 0; i--) {
+            int current = input[i];
+            sorted[c[current] - 1] = current;
+            c[current] -= 1;
+        }
+
+        return sorted;
+    }
+
+    static int[] countElements(int[] input, int k) {
+        int[] c = new int[k + 1];
+        Arrays.fill(c, 0);
+        for (int i : input) {
+            c[i] += 1;
+        }
+
+        for (int i = 1; i < c.length; i++) {
+            c[i] += c[i - 1];
+        }
+        return c;
+    }
+
+    private static void verifyPreconditions(int[] input, int k) {
+        if (input == null) {
+            throw new IllegalArgumentException("Input is required");
+        }
+
+        int min = IntStream.of(input).min().getAsInt();
+        int max = IntStream.of(input).max().getAsInt();
+
+        if (min < 0 || max > k) {
+            throw new IllegalArgumentException("The input numbers should be between zero and " + k);
+        }
+    }
+}
@@ -0,0 +1,25 @@
+package com.baeldung.algorithms.inoutsort;
+
+public class InOutSort {
+
+    public static int[] reverseInPlace(int A[]) {
+        int n = A.length;
+        for (int i = 0; i < n / 2; i++) {
+            int temp = A[i];
+            A[i] = A[n - 1 - i];
+            A[n - 1 - i] = temp;
+        }
+
+        return A;
+    }
+
+    public static int[] reverseOutOfPlace(int A[]) {
+        int n = A.length;
+        int[] B = new int[n];
+        for (int i = 0; i < n; i++) {
+            B[n - i - 1] = A[i];
+        }
+
+        return B;
+    }
+}
@@ -0,0 +1,53 @@
+package com.baeldung.algorithms.radixsort;
+
+import java.util.Arrays;
+
+public class RadixSort {
+
+    public static void sort(int numbers[]) {
+        int maximumNumber = findMaximumNumberIn(numbers);
+
+        int numberOfDigits = calculateNumberOfDigitsIn(maximumNumber);
+
+        int placeValue = 1;
+
+        while (numberOfDigits-- > 0) {
+            applyCountingSortOn(numbers, placeValue);
+            placeValue *= 10;
+        }
+    }
+
+    private static void applyCountingSortOn(int[] numbers, int placeValue) {
+        int range = 10; // radix or the base
+
+        int length = numbers.length;
+        int[] frequency = new int[range];
+        int[] sortedValues = new int[length];
+
+        for (int i = 0; i < length; i++) {
+            int digit = (numbers[i] / placeValue) % range;
+            frequency[digit]++;
+        }
+
+        for (int i = 1; i < range; i++) {
+            frequency[i] += frequency[i - 1];
+        }
+
+        for (int i = length - 1; i >= 0; i--) {
+            int digit = (numbers[i] / placeValue) % range;
+            sortedValues[frequency[digit] - 1] = numbers[i];
+            frequency[digit]--;
+        }
+
+        System.arraycopy(sortedValues, 0, numbers, 0, length);
+    }
+
+    private static int calculateNumberOfDigitsIn(int number) {
+        return (int) Math.log10(number) + 1; // valid only if number > 0
+    }
+
+    private static int findMaximumNumberIn(int[] arr) {
+        return Arrays.stream(arr).max().getAsInt();
+    }
+
+}
@@ -1,4 +1,4 @@
-package com.baeldung.algorithms.stringsortingbynumber;
+package com.baeldung.algorithms.sort.bynumber;

 import java.util.Comparator;

@@ -0,0 +1,32 @@
+package com.baeldung.algorithms.counting;
+
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+class CountingSortUnitTest {
+
+    @Test
+    void countElements_GivenAnArray_ShouldCalculateTheFrequencyArrayAsExpected() {
+        int k = 5;
+        int[] input = { 4, 3, 2, 5, 4, 3, 5, 1, 0, 2, 5 };
+
+        int[] c = CountingSort.countElements(input, k);
+        int[] expected = { 1, 2, 4, 6, 8, 11 };
+        assertArrayEquals(expected, c);
+    }
+
+    @Test
+    void sort_GivenAnArray_ShouldSortTheInputAsExpected() {
+        int k = 5;
+        int[] input = { 4, 3, 2, 5, 4, 3, 5, 1, 0, 2, 5 };
+
+        int[] sorted = CountingSort.sort(input, k);
+
+        // Our sorting algorithm and Java's should return the same result
+        Arrays.sort(input);
+        assertArrayEquals(input, sorted);
+    }
+}
@@ -0,0 +1,23 @@
+package com.baeldung.algorithms.inoutsort;
+
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class InOutSortUnitTest {
+
+    @Test
+    public void givenArray_whenInPlaceSort_thenReversed() {
+        int[] input = {1, 2, 3, 4, 5, 6, 7};
+        int[] expected = {7, 6, 5, 4, 3, 2, 1};
+        assertArrayEquals("the two arrays are not equal", expected, InOutSort.reverseInPlace(input));
+    }
+
+    @Test
+    public void givenArray_whenOutOfPlaceSort_thenReversed() {
+        int[] input = {1, 2, 3, 4, 5, 6, 7};
+        int[] expected = {7, 6, 5, 4, 3, 2, 1};
+        assertArrayEquals("the two arrays are not equal", expected, InOutSort.reverseOutOfPlace(input));
+    }
+}
@@ -0,0 +1,16 @@
+package com.baeldung.algorithms.radixsort;
+
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class RadixSortUnitTest {
+
+    @Test
+    public void givenUnsortedArray_whenRadixSort_thenArraySorted() {
+        int[] numbers = { 387, 468, 134, 123, 68, 221, 769, 37, 7 };
+        RadixSort.sort(numbers);
+        int[] numbersSorted = { 7, 37, 68, 123, 134, 221, 387, 468, 769 };
+        assertArrayEquals(numbersSorted, numbers);
+    }
+}
@@ -1,6 +1,6 @@
-package com.baeldung.algorithms.stringsortingbynumber;
+package com.baeldung.algorithms.sort.bynumber;

-import com.baeldung.algorithms.stringsortingbynumber.NaturalOrderComparators;
+import com.baeldung.algorithms.sort.bynumber.NaturalOrderComparators;
 import org.junit.Test;

 import java.util.ArrayList;
--- a/Show More
+++ b/Show More