codewars #63 Sort two arrays (5kyu)

 #63 Sort two arrays

When no more interesting kata can be resolved, I just choose to create the new kata, to solve their own, to enjoy the process --myjinxin2015 said

Description:

Give you two arrays arr1 and arr2. They have the same length(length>=2). The elements of two arrays always be integer.

Sort arr1 according to the ascending order of arr2; Sort arr2 according to the ascending order of arr1. Description is not easy to understand, for example:

 arr1=[5,4,3,2,1], 

 arr2=[6,5,7,8,9]

Let us try to sorting arr1. First, we need know the ascending order of arr2:

 [5,6,7,8,9]

We can see, after sort arr2 to ascending order, some elements' index are changed:

 unsort arr2      ascending order arr2

 [6,5,7,8,9]--->      [5,6,7,8,9]

 index0(6)  --->      index1

 index1(5)  --->      index0

 index2(7)            index2(no change)

 index3(8)            index3(no change)

 index4(9)            index4(no change)

So, wo need according to these changes to sorting arr1:

 unsort arr1          sorted arr1

 [5,4,3,2,1]--->      [4,5,3,2,1]

 index0(5)  --->      index1

 index1(4)  --->      index0

 index2(3)            index2(no change)

 index3(2)            index3(no change)

 index4(1)            index4(no change)

 So: sorted arr1= [4,5,3,2,1]

And then, we sorting arr2 with the same process:

 unsort arr1      ascending order arr1

 [5,4,3,2,1]--->      [1,2,3,4,5]

 index0(5)  --->      index4

 index1(4)  --->      index3

 index2(3)            index2(no change)

 index3(2)  --->      index1

 index4(1)  --->      index0

 unsort arr2          sorted arr2

 [6,5,7,8,9]--->      [9,8,7,5,6]

 index0(6)  --->      index4

 index1(5)  --->      index3

 index2(7)            index2(no change)

 index3(8)  --->      index1

 index4(9)  --->      index0

 So: sorted arr2= [9,8,7,5,6]

Finally, returns the sorted arrays by a 2D array: [sorted arr1, sorted arr2]

Note: In ascending order sorting process(not the final sort), if some elements have same value, sort them according to their index; You can modify the original array, but I advise you not to do that. ;-)

Some Examples and explain

sortArrays([5,4,3,2,1],[6,5,7,8,9]) should return

[[4,5,3,2,1],[9,8,7,5,6]]

sortArrays([2,1,3,4,5],[5,6,7,8,9]) should return

[[2,1,3,4,5],[6,5,7,8,9]]

sortArrays([5,6,9,2,6,5],[3,6,7,4,8,1]) should return

[[5,5,2,6,9,6],[4,3,1,6,8,7]]

import java.util.Comparator;
import java.util.stream.IntStream;

public class ArraySorter {
	
	private static int [] sort(int [] target, int [] sortby ) {
		return IntStream.range(0, target.length).boxed()
			   .sorted(Comparator.comparing(i->sortby[i]))
			   .mapToInt(i->target[i]).toArray();
	}
	public static int[][] sortTwoArrays(int[] arr1, int[] arr2) {
		return new int [][] {sort(arr1,arr2),sort(arr2,arr1)};
	}
}