Sort even numbers in ascending and odd numbers in descending order

Given an array of numbers, need to sort even nos in ascending order and odd nos in descending order. Input is {9,3,5,6,7,8}, output is {6,8,9,7,5,3}.

I tried but in my output, even numbers gets arranged in descending order and odd numbers in ascending.

My Code:

package practice;
import java.util.*;

public class arrange
{
	static void twoWaySort(int arr[], int n)
	{
		for (int i = 0; i < n; i++)
			if ((arr[i] & 1) == 0) 
				arr[i] *= -1;
		Arrays.sort(arr);
		for (int i = 0; i < n; i++)
			if ((arr[i] & 1) == 0)
				arr[i] *= -1;
	}

	public static void main(String[] args)
	{
		int arr[] = { 9,3,5,6,7,8 };

		twoWaySort(arr, arr.length);

		System.out.println(Arrays.toString(arr));
	}
}

You could convert the int[] to an array of Integer, then sort it with a custom Comparator that first looks at parity, then the actual value.

int[] res = Arrays.stream(arr).boxed().sorted(
             Comparator.comparingInt((Integer x) -> x & 1)
              .thenComparingInt(x -> (x & 1) == 0 ? x : -x)).mapToInt(x -> x).toArray();
// you can also copy over res into arr if in-place modification is required

You have three easy options for your code to adapt:

1. make the odd numbers negative temporarily or
2. invert the sort order
3. flip the array at the end

But please note that all methods shown here will let the odd numbers come first in the result!

For variant 1, you have to invert the if condition inside your for loops:

for (int i = 0; i < n; i++) {
    if ((arr[i] & 1) != 0) {
        arr[i] *= -1;
    }
}

For variant 2, you have to specify a Comparator in the sort method:

Arrays.sort(arr, Comparator.reverseOrder());

Please note that for this variant you need to use arrays of Integer as the sort method only takes a Comparator for arrays of objects. No worries about the calculations, auto-(un-)boxing will convert int to Integer and vice versa wherever necessary.

For variant 3 you just add code to reverse the whole result:

for (int i = 0; i < n / 2; i++) {
    int temp = arr[i];
    arr[i] = arr[n - i - 1];
    arr[n - i - 1] = temp;
}

In general you should always use blocks ({}) to increase readability of your code, and the java style for declaring an array is int[] arr instead of int arr[] (although both styles work). This is because int[] is a class, while int is a primitive, and you see that better if the [] are next to the base type.

You would make your method twoWaySort more robust if you don't pass the length of the array as second parameter, but use arr.length inside the method.