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Thread: QuickSort method

  1. #1
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    Default QuickSort method

     
    void quicksort (int[] a, int lo, int hi)
    {
    //  lo is the lower index, hi is the upper index
    //  of the region of array a that is to be sorted
        int i=lo, j=hi, h;
     
        // comparison element x
        int x=a[(lo+hi)/2];
     
        //  partition
        do
        {    
            while (a[i]<x) i++; 
            while (a[j]>x) j--;
            if (i<=j)
            {
                h=a[i]; a[i]=a[j]; a[j]=h;
                i++; j--;
            }
        } while (i<=j);
     
        //  recursion
        if (lo<j) quicksort(a, lo, j);
        if (i<hi) quicksort(a, i, hi);
    }

    Do you guys see anything wrong with this quickSort method? This will not sort.

    Example: If I type:
    2
    4
    1
    3

    I expect the results to be:
    1
    2
    3
    4

    when I hit the "sort" button. But I don't.

    Your help is appreciated!


  2. #2
    Administrator copeg's Avatar
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    Default Re: QuickSort method

    How are you calling the quicksort method? Please provide an SSCCE or demonstration of what the input is, how the method is called, and what the output is.

  3. #3
    Super Moderator Norm's Avatar
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    Default Re: QuickSort method

    What results do you get for the input you show?

    Try debugging your code by adding printlns to show the logic flow and how variable values change.
    Be sure to add id Strings to the prints to be able to identify them.

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