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Thread: Java Quick Sort Optimization

  1. #1
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    Default Java Quick Sort Optimization

    I have three classes. Each creates an array of 1000 int values.
    class a: uses QuickSort
    class b: uses QuickSort until the size of each partition is <10 then executes InsertSort for sorting the smaller partitions.
    class c: (this is the one I'm having trouble with): same as class b except executes InsertSort on the whole almost sorted array.
    It would seem that class c is only a slight variation of the code in class b (which basically adds to class a). Am I doing this all wrong? Help! Thanks in advanced...

    Class a:

    import java.util.Arrays;
    import java.util.Random;
     
    public class QuickSort {
     
    	static long StartTime = System.nanoTime();
     
    	private static final Random random = new Random();
    	private static final int RANDOM_INT_RANGE = 9999;
     
    	private static int[] randomArray(int size) {
     
    		// Randomize data (array)
    		final int[] arr = new int[size];
    		for (int i = 0; i < arr.length; i++) {
    			arr[i] = random.nextInt(RANDOM_INT_RANGE);
    		}
    		return arr;
    	}
     
    	// Sort
    	private static void sort(int[] arr) {
    		if (arr.length > 0)
    			sortInPlace(arr, 0, arr.length - 1);
    	}
     
    	private static void sortInPlace(int[] arr, int left, int right) {
     
    		if (left >= right)
    			return; // sorted
     
    		final int range = right - left + 1;
    		int pivot = random.nextInt(range) + left;
     
    		int newPivot = partition(arr, left, right, pivot);
     
    		sortInPlace(arr, left, newPivot - 1);
    		sortInPlace(arr, newPivot + 1, right);
     
    	}
     
    	private static int partition(int[] arr, int left, int right, int pivot) {
     
    		int pivotVal = arr[pivot];
    		swapArrayVals(arr, pivot, right);
     
    		int storeIndex = left;
    		for (int i = left; i <= (right - 1); i++) {
    			if (arr[i] < pivotVal) {
    				swapArrayVals(arr, i, storeIndex);
    				storeIndex++;
    			}
    		}
     
    		swapArrayVals(arr, storeIndex, right);
     
    		return storeIndex;
    	}
     
    	static long FinishTime = System.nanoTime();
    	static long TotalTime = FinishTime - StartTime;
     
    	private static void swapArrayVals(int[] arr, int from, int to) {
    		int fromVal = arr[from];
    		int toVal = arr[to];
    		arr[from] = toVal;
    		arr[to] = fromVal;
    	}
     
    	public static void main(String[] args) {
     
    		// Array size
    		int[] arr = randomArray(1000);
    		int[] copy = Arrays.copyOf(arr, arr.length);
     
    		// Print original data (array)
    		System.out.println("The starting/unsorted array: \n"
    				+ Arrays.toString(arr));
     
    		sort(arr);
     
    		// check the result
    		Arrays.sort(copy);
    		if (Arrays.equals(arr, copy)) {
    			System.out.println("The ending/sorted array: \n"
    					+ Arrays.toString(arr));
    			System.out.println("Total elapsed time (milliseconds) " + "is: "
    					+ TotalTime);
     
    		}
     
    	}
    }


    Class b:

    import java.util.Arrays;
    import java.util.Random;
     
    public class OptQSort1 {
     
    	static long StartTime = System.nanoTime();
     
    	private static final Random random = new Random();
    	private static final int RANDOM_INT_RANGE = 9999;
     
    	private static int[] randomArray(int size) {
     
    		// Randomize data (array)
    		final int[] arr = new int[size];
    		for (int i = 0; i < arr.length; i++) {
    			arr[i] = random.nextInt(RANDOM_INT_RANGE);
    		}
    		return arr;
    	}
     
    	// Sort
    	private static void sort(int[] arr) {
    		if (arr.length > 0)
    			sortInPlace(arr, 0, arr.length - 1);
     
    		insertionSort(arr, 0, arr.length - 1);
    	}
     
    	private static void sortInPlace(int[] arr, int left, int right) {
     
    		// OptQSort1:
    		int size = right - left + 1;
    		if (size < 10)
    			insertionSort(arr, left, right);
     
    		if (left >= right)
    			return; // sorted
     
    		final int range = right - left + 1;
    		int pivot = random.nextInt(range) + left;
     
    		int newPivot = partition(arr, left, right, pivot);
     
    		sortInPlace(arr, left, newPivot - 1);
    		sortInPlace(arr, newPivot + 1, right);
     
    	}
     
    	private static int partition(int[] arr, int left, int right, int pivot) {
     
    		int pivotVal = arr[pivot];
    		swapArrayVals(arr, pivot, right);
     
    		int storeIndex = left;
    		for (int i = left; i <= (right - 1); i++) {
    			if (arr[i] < pivotVal) {
    				swapArrayVals(arr, i, storeIndex);
    				storeIndex++;
    			}
    		}
     
    		swapArrayVals(arr, storeIndex, right);
     
    		return storeIndex;
    	}
     
    	private static void swapArrayVals(int[] arr, int from, int to) {
    		int fromVal = arr[from];
    		int toVal = arr[to];
    		arr[from] = toVal;
    		arr[to] = fromVal;
    	}
     
    	public static void insertionSort(int[] arr, int left, int right) {
    		int in, out;
     
    		for (out = left + 1; out <= right; out++) {
    			int temp = arr[out];
    			in = out;
     
    			while (in > left && arr[in - 1] >= temp) {
    				arr[in] = arr[in - 1];
    				--in;
    			}
    			arr[in] = temp;
    		}
     
    	}
     
    	static long FinishTime = System.nanoTime();
    	static long TotalTime = FinishTime - StartTime;
     
    	public static void main(String[] args) {
     
    		// Array size
    		int[] arr = randomArray(1000);
    		int[] copy = Arrays.copyOf(arr, arr.length);
     
    		// Print original data (array)
    		System.out.println("The starting/unsorted array: \n"
    				+ Arrays.toString(arr));
     
    		sort(arr);
     
    		// check the result
    		Arrays.sort(copy);
    		if (Arrays.equals(arr, copy)) {
    			System.out.println("The ending/sorted array: \n"
    					+ Arrays.toString(arr));
    			System.out.println("Total elapsed time (milliseconds) " + "is: "
    					+ TotalTime);
     
    		}
    	}
     
    }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Java Quick Sort Optimization

    Please explain your problem? Does the code compile?
    Do you get errors when executing?
    Is the results incorrect?
    Show the output and explain what is wrong with it and what it should be.

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