import java.util.Arrays;

public class ConvertArray {

public int getOriginalIndex(int currentIndex, int length) {

return (currentIndex % 3) * length + currentIndex/3;

}

public int[] convert(int[] input) {

// When array size is less than 3, returns an error.

if (input.length % 3 != 0 ) {

System.out.println("Error! Array cannot be divided into three equal parts");

return;

}

for (int i = 0; i < input.length; ++i) {

int originalIndex = getOriginalIndex(i, input.length/3);

while (originalIndex < i) {

originalIndex = getOriginalIndex(originalIndex, input.length/3);

}

int temp = input[i];

input[i] = input[originalIndex];

input[originalIndex] = temp;

}

return input;

}

public static void main(String[] args) {

ConvertArray c = new ConvertArray();

int[] test1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

System.out.println(Arrays.toString(c.convert(test1)));

}

}