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BAEL-3484: Partitioning and Sorting an Array With Many Repeated Entries (eugenp#8369)
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‎algorithms-sorting-2/.gitignore‎

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/target/
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.settings/
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.classpath
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.project

‎algorithms-sorting-2/pom.xml‎

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<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<artifactId>algorithms-sorting-2</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<name>algorithms-sorting-2</name>
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<parent>
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<groupId>com.baeldung</groupId>
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<artifactId>parent-modules</artifactId>
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<version>1.0.0-SNAPSHOT</version>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-math3</artifactId>
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<version>${commons-math3.version}</version>
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</dependency>
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<dependency>
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<groupId>commons-codec</groupId>
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<artifactId>commons-codec</artifactId>
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<version>${commons-codec.version}</version>
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</dependency>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<version>${lombok.version}</version>
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<scope>provided</scope>
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</dependency>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-api</artifactId>
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<version>${junit-jupiter-api.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${org.assertj.core.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<pluginManagement>
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<plugins>
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<plugin>
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<groupId>org.codehaus.mojo</groupId>
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<artifactId>exec-maven-plugin</artifactId>
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<version>${exec-maven-plugin.version}</version>
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</plugin>
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</plugins>
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</pluginManagement>
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</build>
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<properties>
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<commons-math3.version>3.6.1</commons-math3.version>
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<org.assertj.core.version>3.9.0</org.assertj.core.version>
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<commons-codec.version>1.11</commons-codec.version>
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<junit-jupiter-api.version>5.3.1</junit-jupiter-api.version>
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</properties>
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</project>

‎algorithms-sorting-2/src/main/java/com/baeldung/algorithms/quicksort/BentleyMcIlroyPartioning.java‎

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package com.baeldung.algorithms.quicksort;
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import static com.baeldung.algorithms.quicksort.SortingUtils.swap;
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public class BentleyMcIlroyPartioning {
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public static Partition partition(int input[], int begin, int end) {
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int left = begin, right = end;
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int leftEqualKeysCount = 0, rightEqualKeysCount = 0;
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int partitioningValue = input[end];
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while (true) {
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while (input[left] < partitioningValue)
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left++;
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while (input[right] > partitioningValue) {
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if (right == begin)
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break;
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right--;
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}
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if (left == right && input[left] == partitioningValue) {
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swap(input, begin + leftEqualKeysCount, left);
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leftEqualKeysCount++;
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left++;
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}
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if (left >= right) {
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break;
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}
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swap(input, left, right);
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if (input[left] == partitioningValue) {
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swap(input, begin + leftEqualKeysCount, left);
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leftEqualKeysCount++;
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}
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if (input[right] == partitioningValue) {
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swap(input, right, end - rightEqualKeysCount);
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rightEqualKeysCount++;
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}
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left++; right--;
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}
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right = left - 1;
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for (int k = begin; k < begin + leftEqualKeysCount; k++, right--) {
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if (right >= begin + leftEqualKeysCount)
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swap(input, k, right);
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}
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for (int k = end; k > end - rightEqualKeysCount; k--, left++) {
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if (left <= end - rightEqualKeysCount)
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swap(input, left, k);
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}
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return new Partition(right + 1, left - 1);
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}
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public static void quicksort(int input[], int begin, int end) {
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if (end <= begin)
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return;
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Partition middlePartition = partition(input, begin, end);
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quicksort(input, begin, middlePartition.getLeft() - 1);
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quicksort(input, middlePartition.getRight() + 1, end);
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}
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}

‎algorithms-sorting-2/src/main/java/com/baeldung/algorithms/quicksort/DutchNationalFlagPartioning.java‎

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package com.baeldung.algorithms.quicksort;
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import static com.baeldung.algorithms.quicksort.SortingUtils.compare;
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import static com.baeldung.algorithms.quicksort.SortingUtils.swap;
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public class DutchNationalFlagPartioning {
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public static Partition partition(int[] a, int begin, int end) {
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int lt = begin, current = begin, gt = end;
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int partitioningValue = a[begin];
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while (current <= gt) {
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int compareCurrent = compare(a[current], partitioningValue);
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switch (compareCurrent) {
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case -1:
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swap(a, current++, lt++);
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break;
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case 0:
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current++;
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break;
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case 1:
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swap(a, current, gt--);
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break;
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}
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}
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return new Partition(lt, gt);
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}
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public static void quicksort(int[] input, int begin, int end) {
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if (end <= begin)
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return;
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Partition middlePartition = partition(input, begin, end);
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quicksort(input, begin, middlePartition.getLeft() - 1);
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quicksort(input, middlePartition.getRight() + 1, end);
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}
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}

‎algorithms-sorting-2/src/main/java/com/baeldung/algorithms/quicksort/Partition.java‎

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package com.baeldung.algorithms.quicksort;
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public class Partition {
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private int left;
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private int right;
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public Partition(int left, int right) {
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super();
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this.left = left;
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this.right = right;
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}
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public int getLeft() {
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return left;
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}
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public void setLeft(int left) {
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this.left = left;
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}
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public int getRight() {
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return right;
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}
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public void setRight(int right) {
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this.right = right;
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}
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}

‎algorithms-sorting-2/src/main/java/com/baeldung/algorithms/quicksort/SortingUtils.java‎

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package com.baeldung.algorithms.quicksort;
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public class SortingUtils {
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public static void swap(int[] array, int position1, int position2) {
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if (position1 != position2) {
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int temp = array[position1];
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array[position1] = array[position2];
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array[position2] = temp;
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}
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}
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public static int compare(int num1, int num2) {
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if (num1 > num2)
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return 1;
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else if (num1 < num2)
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return -1;
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else
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return 0;
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}
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public static void printArray(int[] array) {
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if (array == null) {
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return;
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}
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for (int e : array) {
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System.out.print(e + " ");
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}
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System.out.println();
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}
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}

‎algorithms-sorting-2/src/main/resources/logback.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<configuration>
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<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
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<encoder>
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<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
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</pattern>
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</encoder>
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</appender>
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<root level="INFO">
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<appender-ref ref="STDOUT"/>
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</root>
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</configuration>

‎algorithms-sorting-2/src/test/java/com/baeldung/algorithms/quicksort/BentleyMcilroyPartitioningUnitTest.java‎

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package com.baeldung.algorithms.quicksort;
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import org.junit.Assert;
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import org.junit.Test;
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public class BentleyMcilroyPartitioningUnitTest {
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@Test
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public void given_IntegerArray_whenSortedWithBentleyMcilroyPartitioning_thenGetSortedArray() {
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int[] actual = {3, 2, 2, 2, 3, 7, 7, 3, 2, 2, 7, 3, 3};
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int[] expected = {2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 7, 7, 7};
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BentleyMcIlroyPartioning.quicksort(actual, 0, actual.length - 1);
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Assert.assertArrayEquals(expected, actual);
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}
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}

‎algorithms-sorting-2/src/test/java/com/baeldung/algorithms/quicksort/DNFThreeWayQuickSortUnitTest.java‎

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package com.baeldung.algorithms.quicksort;
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import org.junit.Assert;
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import org.junit.Test;
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public class DNFThreeWayQuickSortUnitTest {
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@Test
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public void givenIntegerArray_whenSortedWithThreeWayQuickSort_thenGetSortedArray() {
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int[] actual = {3, 5, 5, 5, 3, 7, 7, 3, 5, 5, 7, 3, 3};
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int[] expected = {3, 3, 3, 3, 3, 5, 5, 5, 5, 5, 7, 7, 7};
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DutchNationalFlagPartioning.quicksort(actual, 0, actual.length - 1);
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Assert.assertArrayEquals(expected, actual);
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}
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}

‎pom.xml‎

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<module>algorithms-miscellaneous-4</module>
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<module>algorithms-miscellaneous-5</module>
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<module>algorithms-sorting</module>
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<module>algorithms-sorting-2</module>
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<module>algorithms-searching</module>
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<module>animal-sniffer-mvn-plugin</module>
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<module>annotations</module>
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<module>algorithms-miscellaneous-4</module>
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<module>algorithms-miscellaneous-5</module>
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<module>algorithms-sorting</module>
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<module>algorithms-sorting-2</module>
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<module>algorithms-searching</module>
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<module>animal-sniffer-mvn-plugin</module>
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<module>annotations</module>

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