Question

I am creating quicksort to sort other city nearest to a specific city.

Here is my code:

    private static void QuickSort(ArrayList<City> array, int First, int Last, City city ){
    int Low,High,MidDistance;
    Low = First;
    High = Last;
    Edge compareEdge = new Edge(array.get((First + Last)/ 2), city);
    MidDistance = compareEdge.computeDistance();

    do {
        compareEdge = new Edge(array.get(Low),city);
        while (compareEdge.computeDistance() < MidDistance){
            Low += 1;
            compareEdge = new Edge(array.get(Low),city);
        }

        compareEdge = new Edge(array.get(High),city);
        while (compareEdge.computeDistance() > MidDistance){
            High -= 1;
            compareEdge = new Edge(array.get(High),city);
        }

        if (Low <= High) {
                Swap(array,Low,High);
                Low = Low + 1;
                High = High - 1;
        }

    } while (Low <= High);

    if (First < High){
        QuickSort(array, First, High, city);
    }

    if (Low < Last){
        QuickSort(array, Low, Last, city);
    }

}

private static void Swap(ArrayList<City>array,int Low, int High){
    City tempCtiy = array.get(Low);
    array.get(Low).set(array.get(High));
    array.get(High).set(tempCtiy);
}

This code is inside my MST class. so when I run it

Exception in thread “main” java.lang.IndexOutOfBoundsException: Index: 49, Size: 49

it happens here :

    while (compareEdge.computeDistance() < MidDistance){
        Low += 1;
        compareEdge = new Edge(array.get(Low),city);
    }

Help me to figure out what’s wrong.
It works well when I write in VB.net.

Answer 1

Add the termination condition in while on Low as below:

      while (compareEdge.computeDistance() < MidDistance &&
              && Low < array.size()-1){
              Low += 1;
              compareEdge = new Edge(array.get(Low),city);
      }