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Author: Jubayer Alam

bin/Quicksort.class

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+public class Quicksort  {
+	private int[] numbers;
+	private int number;
+	public void sort(int[] values) { //S1
+        // check for empty or null array
+		if (values ==null || values.length==0){ //C1
+            return; //S2
+        }
+		this.numbers = values; //S3
+        number = values.length; //S4
+        quicksort(0, number - 1); //S5
+    }
+	private void quicksort(int low, int high) {
+		int i = low, j = high; //S6
+        // get the pivot element from the middle of the list
+		int pivot = numbers[low + (high-low)/2]; //S7
+        // divide into two lists
+		while (i <= j) { //C2
+            // if the current value from the left list is smaller than the pivot
+            // element then get the next element from the left list
+			while (numbers[i] < pivot) { //C3 
+                i++; //S8
+            }
+            // if the current value from the right list is larger than the pivot
+            // element then get the next element from the right list
+			while (numbers[j] > pivot) { //C4
+                j--; //S9
+            }
+
+            // if we have found a value in the left list which is larger than
+            // the pivot element and if we have found a value in the right list
+            // which is smaller than the pivot element then we exchange the
+            // values.
+            // as we are done we can increase i and j
+			if (i <= j) { //C5
+                exchange(i, j); //S10
+                i++; //S11
+                j--; //S12
+            }
+        }
+        // recursion method
+		if (low < j) //C6
+            quicksort(low, j); //S13
+        if (i < high) //C7
+            quicksort(i, high); //S14
+    }
+	private void exchange(int i, int j) {
+        int temp = numbers[i];
+        numbers[i] = numbers[j];
+        numbers[j] = temp;
+    }
+}

bin/QuicksortTest.class

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+import java.util.Arrays;
+import java.util.Random;
+import org.junit.Before;
+import org.junit.Test;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+public class QuicksortTest {
+	private int[] numbers;
+    private final static int SIZE = 7;
+    private final static int MAX = 15;
+    @Before
+    public void setUp() throws Exception {
+        numbers = new int[SIZE];
+        Random generator = new Random();
+        for (int i = 0; i < numbers.length; i++) {
+            numbers[i] = generator.nextInt(MAX);
+        }
+    }
+    @Test
+    public void testNull() {
+        Quicksort sorter = new Quicksort();
+        sorter.sort(null);
+    }
+    @Test
+    public void testEmpty() {
+        Quicksort sorter = new Quicksort();
+        sorter.sort(new int[0]);
+    }
+    @Test
+    public void testSimpleElement() {
+        Quicksort sorter = new Quicksort();
+        int[] test = new int[1];
+        test[0] = 7;
+        sorter.sort(test);
+        }
+    @Test
+    public void testSpecial() {
+        Quicksort sorter = new Quicksort();
+        int[] test = { 8,9,13,14,1,3,6,12,10,2,11,4,5,7,15 };
+        sorter.sort(test);
+        if (!validate(test)) {
+            fail("Should not happen");
+        }
+        printResult(test);
+    }
+    @Test
+    public void testQuickSort() {
+    	for (Integer i : numbers) {
+            System.out.println(i + " ");
+        }
+    	long startTime = System.currentTimeMillis();
+    	Quicksort sorter = new Quicksort();
+        sorter.sort(numbers);
+        long stopTime = System.currentTimeMillis();
+        long elapsedTime = stopTime - startTime;
+        System.out.println("Quicksort " + elapsedTime);
+        if (!validate(numbers)) {
+            fail("Should not happen");
+        }
+        assertTrue(true);
+    }
+    @Test
+    public void testStandardSort() {
+    	long startTime = System.currentTimeMillis();
+        Arrays.sort(numbers);
+        long stopTime = System.currentTimeMillis();
+        long elapsedTime = stopTime - startTime;
+        System.out.println("Standard Java sort " + elapsedTime);
+        if (!validate(numbers)) {
+            fail("Should not happen");
+        }
+        assertTrue(true);
+    }
+    private boolean validate(int[] numbers) {
+        for (int i = 0; i < numbers.length - 1; i++) {
+            if (numbers[i] > numbers[i + 1]) {
+                return false;
+            }
+        }
+        return true;
+    }
+    private void printResult(int[] numbers) {
+        for (int i = 0; i < numbers.length; i++) {
+            System.out.print(numbers[i]);
+        }
+        System.out.println();
+    }
+}