Step 1: Implement the getSortedRunLength() method

Implement the getSortedRunLength() method in NaturalMergeSorter.java. Access NaturalMergeSorter.java by clicking on the orange arrow next to NaturalMerge.java at the top of the coding window.

getSortedRunLength() has three parameters:

array: a reference to an array of integers,

arrayLength: an integer for the array's length, and

startIndex: an integer for the run's starting index.

The method returns the number of array elements sorted in ascending order, starting at startIndex and ending either at the end of the sorted run, or the end of the array, whichever comes first. The method returns 0 if startIndex is out of bounds.

File NaturalMerge.java has several test cases for getSortedRunLength() that can be run by clicking the "Run program" button. One test case also exists for naturalMergeSort(), but that can be ignored until step two is completed.

Step 2: Implement the naturalMergeSort() method

Implement the naturalMergeSort() method in NaturalMergeSorter.java. naturalMergeSort() must:

1. Start at index i=0

2. Get the length of the first sorted run, starting at i

Return if the first run's length equals the array length

If the first run ends at the array's end, reassign i=0 and repeat step 2

3. Get the length of the second sorted run, starting immediately after the first

4. Merge the two runs with the provided merge() method

5. Reassign i with the first index after the second run, or 0 if the second run ends at the array's end

6. Go to step 2

NaturalMerge.java:

import java.io.PrintWriter; import java.util.Arrays;

public class NaturalMerge { public static void main(String[] args) { // Test case array: A completely sorted array int[] arr1 = { 15, 23, 23, 23, 31, 64, 77, 87, 88, 91 }; int arr1Length = arr1.length; // Test case array: Sorted run of 3 followed by sorted run of 6 int[] arr2 = { 64, 88, 91, 12, 21, 34, 43, 56, 65 }; int arr2Length = arr2.length; // Test case array: 5 elements in descending order, so 5 runs of length 1 int[] arr3 = { -10, -20, -30, -40, -50 }; int arr3Length = arr3.length; // Test case array: 8 equal elements, so 1 run of 8 int[] arr4 = { -99, -99, -99, -99, -99, -99, -99, -99 }; int arr4Length = arr4.length; // Test cases: RunLengthTestCase[] testCases = { // First test case uses an out-of-bounds starting index. Remaining test // cases do not. new RunLengthTestCase(arr1, arr1Length, arr1Length, 0), new RunLengthTestCase(arr1, arr1Length, 0, arr1Length), new RunLengthTestCase(arr1, arr1Length, 3, arr1Length - 3), new RunLengthTestCase(arr2, arr2Length, 0, 3), new RunLengthTestCase(arr2, arr2Length, 2, 1), new RunLengthTestCase(arr2, arr2Length, 3, 6), new RunLengthTestCase(arr3, arr3Length, 0, 1), new RunLengthTestCase(arr3, arr3Length, 3, 1), new RunLengthTestCase(arr4, arr4Length, 0, arr4Length), new RunLengthTestCase(arr4, arr4Length, 4, arr4Length - 4), new RunLengthTestCase(arr4, arr4Length, 5, arr4Length - 5) }; // Execute each test case PrintWriter testFeedback = new PrintWriter(System.out); int testCasesLength = testCases.length; for (int i = 0; i < testCasesLength; i++) { RunLengthTestCase testCase = testCases[i]; // Execute the test case, using System.out to write messages testCase.execute(testFeedback); } testFeedback.flush(); // Test case array for sorting int[] arr5 = { 92, 71, 18, 26, 54, 73, 89, 10, 39, 99, 64, 22 }; int arr5Length = arr5.length; int[] arr5Copy = new int[arr5Length]; for (int i = 0; i < arr5Length; i++) { arr5Copy[i] = arr5[i]; }

NaturalMergeSorter sorter = new NaturalMergeSorter(); sorter.naturalMergeSort(arr5Copy, arr5Length); System.out.print(" "); System.out.print((IsArraySorted.isSorted(arr5Copy, arr5Length) ? "PASS" : "FAIL")); System.out.print(": naturalMergeSort()"); System.out.print(" "); System.out.print(" Array before calling naturalMergeSort(): " + Arrays.toString(arr5)); System.out.print(" "); System.out.print(" Array after calling naturalMergeSort(): " + Arrays.toString(arr5Copy)); System.out.print(" "); } }

NaturalMergeSorter.java

public class NaturalMergeSorter { public int getSortedRunLength(int[] array, int arrayLength, int startIndex) { // Your code here }

public void naturalMergeSort(int[] array, int arrayLength) { // Your code here } public void merge(int[] numbers, int leftFirst, int leftLast, int rightLast) { int mergedSize = rightLast - leftFirst + 1; int[] mergedNumbers = new int[mergedSize]; int mergePos = 0; int leftPos = leftFirst; int rightPos = leftLast + 1; // Add smallest element from left or right partition to merged numbers while (leftPos <= leftLast && rightPos <= rightLast) { if (numbers[leftPos] <= numbers[rightPos]) { mergedNumbers[mergePos] = numbers[leftPos]; leftPos++; } else { mergedNumbers[mergePos] = numbers[rightPos]; rightPos++; } mergePos++; } // If left partition isn't empty, add remaining elements to mergedNumbers while (leftPos <= leftLast) { mergedNumbers[mergePos] = numbers[leftPos]; leftPos++; mergePos++; } // If right partition isn't empty, add remaining elements to mergedNumbers while (rightPos <= rightLast) { mergedNumbers[mergePos] = numbers[rightPos]; rightPos++; mergePos++; } // Copy merged numbers back to numbers for (mergePos = 0; mergePos < mergedSize; mergePos++) { numbers[leftFirst + mergePos] = mergedNumbers[mergePos]; } // Free temporary array mergedNumbers = null; } }

RunLengthTestCase.java

import java.io.PrintWriter; import java.util.Arrays;

// RunLengthTestCase represents a test case for the NaturalMergeSorter class's // getSortedRunLength() function. public class RunLengthTestCase { public int[] array; public int arrayLength; public int startIndex; public int expectedReturnValue;

public RunLengthTestCase(int[] array, int len, int start, int expectedRet) { this.array = array; arrayLength = len; startIndex = start; expectedReturnValue = expectedRet; } // Executes the test case. If the test case passes, a message that starts // with "PASS" is printed and true is returned. Otherwise a message that // starts with "FAIL" is printed and false is returned. public final boolean execute(PrintWriter testFeedback) { // Create a NaturalMergeSorter instance NaturalMergeSorter userSorter = new NaturalMergeSorter(); // Call the getSortedRunLength() method with the test case parameters int userRetVal = userSorter.getSortedRunLength( array, arrayLength, startIndex); // The test passed only if the actual return value equals the expected // return value final boolean passed = (userRetVal == expectedReturnValue); // Show a message about the test case's results if(passed) { testFeedback.write("PASS: "); } else { testFeedback.write("FAIL: "); } testFeedback.write("getSortedRunLength()" + " "); testFeedback.write(" Array: " + Arrays.toString(array) + " "); testFeedback.write(" Start index: " + startIndex + " "); testFeedback.write(" Expected return value: " + expectedReturnValue); testFeedback.write(" "); testFeedback.write(" Actual return value: " + userRetVal + " "); return passed; }

// Writes comma-separated elements to PrintWriter public final void writeArray(PrintWriter output) { // Output occurs only if at least one array element exists if (arrayLength > 0) { // Write the first element without a comma output.write("" + array[0]); // Write each remaining element preceded by a comma for (int i = 1; i < arrayLength; i++) { output.write(", " + array[i]); } } } }

IsArraySorted.java

public class IsArraySorted { public static boolean isSorted(int[] arr, int arrSize) { for (int i = 1; i < arrSize; i++) { if (arr[i] < arr[i - 1]) { return false; } } return true; } }