about Quick Sort

Posted by matin1234 on Stack Overflow See other posts from Stack Overflow or by matin1234
Published on 2010-06-08T07:46:28Z Indexed on 2010/06/08 7:52 UTC
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Hi I have written this code but it will print these stack traces in the console please help me thanks! (Aslo "p" and "q" are the first and last index of our array ,respectively)

public class JavaQuickSort {

public static void QuickSort(int A[], int p, int q) {
    int i, last = 0;

    Random rand = new Random();
    if (q < 1) {
        return;
    }
    **swap(A, p, rand.nextInt() % (q+1));**

    for (i = p + 1; i <= q; i++) {
        if (A[i] < A[p]) {
            swap(A, ++last, i);
        }

    }
    swap(A, p, last);
    QuickSort(A, p, last - 1);
    QuickSort(A, last + 1, q);
}

private static void swap(int[] A, int i, int j) {
    int temp;
    temp = A[i];
    **A[i] = A[j];**
    A[j] = temp;


}
public static void main(String[] args){
    int[] A = {2,5,7,3,9,0,1,6,8};
    **QuickSort(A, 0,8 );**
    System.out.println(Arrays.toString(A));
}
}

the Stack traces :

run:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -3
        at JavaQuickSort.swap(JavaQuickSort.java:38)
        at JavaQuickSort.QuickSort(JavaQuickSort.java:22)
        at JavaQuickSort.main(JavaQuickSort.java:45)
Java Result: 1
BUILD SUCCESSFUL (total time: 2 seconds)

I also bold those statements that cause these stack traces. like ==> ** ...**

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