/*
 * Java program to test/time quicksort.
 *
 * sequential version.
 *
 * command-line arguments:  number of elements to sort, seed for RNG.
 */
package csci3366.hw4;

import java.util.Random;

public class QuickSortSeq {

    /* main method */

    public static void main(String[] args) {

        String usageMsg = "arguments are numElements seed";

        /* process command-line arguments */
        if (args.length < 2) {
            System.err.println(usageMsg);
            System.exit(1);
        }
        int n = 0;
        int seed = 0;
        try {
            n = Integer.parseInt(args[0]);
            seed = Integer.parseInt(args[1]);
        }
        catch (NumberFormatException e) {
            System.err.println("arguments must be integers");
            System.exit(1);
        }

        /* generate data */
        Integer[] ints = new Integer[n];
        Random randGen = new Random((long) seed);
        for (int i = 0; i < ints.length; ++i) {
            ints[i] = new Integer(randGen.nextInt());
        }

        /* sort (time this part only) */
        long startTime = System.currentTimeMillis();
        sort(ints);
        long endTime = System.currentTimeMillis();

        /* check whether sort succeeded */
        if (isSorted(ints)) {
            System.out.println("sort succeeded");
        }
        else {
            System.out.println("sort failed");
        }

        /* print timing result */
        System.out.println("Sequential program");
        System.out.println("Time for sort of " + n + 
                " random integers (seed " + seed + ") is " +
                ((double) (endTime - startTime) / 1000) + " seconds");
    }

    /* check whether array is sorted */
    public static boolean isSorted(Integer[] data) {
        for (int i = 0; i < data.length-1; ++i) {
            if (data[i].compareTo(data[i+1]) > 0)
                return false;
        }
        return true;
    }

    /* main quicksort routine */
    public static void sort(Integer[] data) { 
        sort(data, 0, data.length-1);
    }

    /*
     * recursive quicksort:
     *   sorts data[firstIndex..lastIndex] in place
     */
    private static void sort(Integer[] data, int startIndex, int endIndex) {
        if (startIndex < endIndex) {
            int splitIndex = partition(data, startIndex, endIndex);
            sort(data, startIndex, splitIndex-1);
            sort(data, splitIndex+1, endIndex);
        }
    }

    /*
     * rearranges array elements from startIndex through endIndex such that
     *   elements <= pivot are to the left of splitIndex and elements > pivot
     *   are to the right of splitIndex, places pivot at splitIndex, and
     *   returns splitIndex.
     */
    private static int partition(Integer[] data, int startIndex, int endIndex) {

        int k = startIndex + 1;
        int m = startIndex + 1;
		
        /*
         * loop invariant:
         * data[startIndex .. k-1] <= data[startIndex]
         * data[k .. m-1] > data[startIndex]
         */
        while (m <= endIndex) {
            if (data[m].compareTo(data[startIndex]) > 0) { }
            else {
                swap(data, k, m);
                ++k;
            }
            ++m;
        }
        swap(data, startIndex, k-1);
        return k-1;
    }

    /* swaps array elements */
    private static void swap(Integer[] data, int i, int j) {
        Integer temp = data[i];
        data[i] = data[j];
        data[j] = temp;
    }
}