Sorting Parallel Arrays in Java

Question

I have two arrays, one stores the distance of the cities and the other stores the corresponding population. Everything works fine if the distance of the cities is in ascending o

Answer 1

The correct solution is this. However if you want a completely mad hack, you can do this:

public final class ParallelIntArrays extends AbstractList {

    private final int[] array1;
    private final int[] array2;

    public ParallelIntArrays(int[] array1, int[] array2) {
        if (array1.length != array2.length)
            throw new IllegalArgumentException();
        this.array1 = array1;
        this.array2 = array2;
    }

    @Override
    public int[] get(int i) {
        return new int[] { array1[i], array2[i] };
    }

    @Override
    public int size() {
        return array1.length;
    }

    @Override
    public int[] set(int i, int[] a) {
        if (a.length != 2)
            throw new IllegalArgumentException();
        int[] b = get(i);
        array1[i] = a[0];
        array2[i] = a[1];
        return b;
    }
}

Then you can do:

int[] city = {5,   1,  2,    4,   3   };
int[] pop =  {100, 30, 4000, 400, 5000};
new ParallelIntArrays(city, pop).sort(Comparator.comparingInt(arr -> arr[0]));
System.out.println(Arrays.toString(city));
System.out.println(Arrays.toString(pop));

Note that as written above, ParallelIntArrays does not function correctly as a List. For example list.contains(list.get(0)) would give false. If you made it a List or a List> instead, it would be fixed.