How do you sort odd and even array numbers in descending and ascending order?

Question

I need help to sort numbers in an array in ascending and descending order. Even numbers should be ascending and odd numbers descending.

I have managed to sort the number in ascending order but want to do the opposite for the odd numbers.

Actual Results: Both odd and even numbers ascending

Expected Results: Even numbers ascending and odd numbers descending

System.out.println("\n" + "random numbers generated:");
System.out.println(Arrays.toString(arrayList).replace("[", "").replace("]", "").replace(",", ""));
for (int i = 0; i < arrayList.length; i++) {
    for (int j = i+1; j < arrayList.length; j++) {
        if(arrayList[i] > arrayList[j]) {
            temporaryArray = arrayList[i];
            arrayList[i] = arrayList[j];
            arrayList[j] = temporaryArray;
        }
    }
}
System.out.println("\n" + "random numbers arranged:");

int[] arrayTwo = Arrays.copyOf(arrayList, arrayList.length);

for (int i = 0; i < arrayList.length; i++) {
    if(arrayTwo[i]%2!=0) {
        System.out.print(arrayTwo[i] + " ");
    }
}

System.out.print("| ");

for (int i = 0; i < arrayList.length; i++) {
    if(arrayTwo[i]%2==0) {
        System.out.print(arrayTwo[i] + " ");
    }
}

How can I reverse array for odd numbers?

Answer 1

I would recommend that you:

• 1. sort all numbers in ascending order,
• 2. extract the odd numbers to a second array and
• 3. reverse this new array. Manipulating two different orderings in a same array would prove much more complicated. On a side note, if you don't have a requirement not to, I'd recommend using the Arrays library's Arrays.sort() to simplify your code. It is very readable and has lower complexity of O(N log N).

Answer 2

What you can do is write a recursive function like so:

public static void printOddReversed(int[] array, int index) {
    if (index == array.length)
        return;

    printOddReversed(array, index + 1);

    if (array[index] % 2 != 0) {
        System.out.print(array[index] + " ");
    }
}

and then instead of the second loop, call it like so:

printOddReversed(arrayTwo, 0);

Answer 3

A simple way to do that is by using a special comparator:

        if (a%2 == 0) {
            if (b%2 == 0) {
                return Integer.compare(a,b);
            } else {
                return -1;
            }
        } else {
            if (b%2 == 0) {
                return 1;
            } else {
                return Integer.compare(b, a);
            }
        }

UPDATE: Example

    int[] arrayList = {959, 321, 658, 3, 506, 165, 560, 582, 199, 533, 178};
    for (int i = 0; i < arrayList.length; i++) {
        for (int j = i+1; j < arrayList.length; j++) {
            if(compare(arrayList[i], arrayList[j]) > 0) {
                int temporaryArray = arrayList[i];
                arrayList[i] = arrayList[j];
                arrayList[j] = temporaryArray;
            }
        }
    }

    System.out.println(Arrays.toString(arrayList));

...

private static int compare(int a, int b) {
    if (a%2 == 0) {
        if (b%2 == 0) {
            return Integer.compare(a,b);
        } else {
            return -1;
        }
    } else {
        if (b%2 == 0) {
            return 1;
        } else {
            return Integer.compare(b, a);
        }
    }
}

Answer 4

I managed to solve this by just reversing

for (int i = arrayList.length-1;i>=0;i--) {
    if(arrayTwo[i]%2==0) {
        System.out.print(arrayTwo[i] + " ");