QSortAlgorithm.java

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 *
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 * modification, are permitted provided that the following conditions
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 *
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 *     notice, this list of conditions and the following disclaimer.
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 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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/*
 * This source code is provided to illustrate the usage of a given feature
 * or technique and has been deliberately simplified. Additional steps
 * required for a production-quality application, such as security checks,
 * input validation and proper error handling, might not be present in
 * this sample code.
 */
 
 
 
public class QSortAlgorithm extends SortAlgorithm {
 
    private boolean pauseTrue(int lo, int hi) throws Exception {
        super.pause(lo, hi);
        return true;
    }
 
    void QuickSort(int a[], int lo0, int hi0) throws Exception {
        int lo = lo0;
        int hi = hi0;
        int mid;
 
        if (hi0 > lo0) {
 
            /* Arbitrarily establishing partition element as the midpoint of
             * the array.
             */
            mid = a[(lo0 + hi0) / 2];
 
            // loop through the array until indices cross
            while (lo <= hi) {
                /* find the first element that is greater than or equal to
                 * the partition element starting from the left Index.
                 */
                while ((lo < hi0) && pauseTrue(lo0, hi0) && (a[lo] < mid)) {
                    ++lo;
                }
 
                /* find an element that is smaller than or equal to
                 * the partition element starting from the right Index.
                 */
                while ((hi > lo0) && pauseTrue(lo0, hi0) && (a[hi] > mid)) {
                    --hi;
                }
 
                // if the indexes have not crossed, swap
                if (lo <= hi) {
                    swap(a, lo, hi);
                    ++lo;
                    --hi;
                }
            }
 
            /* If the right index has not reached the left side of array
             * must now sort the left partition.
             */
            if (lo0 < hi) {
                QuickSort(a, lo0, hi);
            }
 
            /* If the left index has not reached the right side of array
             * must now sort the right partition.
             */
            if (lo < hi0) {
                QuickSort(a, lo, hi0);
            }
 
        }
    }
 
    private void swap(int a[], int i, int j) {
        int T;
        T = a[i];
        a[i] = a[j];
        a[j] = T;
 
    }
 
    @Override
    public void sort(int a[]) throws Exception {
        QuickSort(a, 0, a.length - 1);
    }
}