# Split and then add both sides of an array together in Java

## The challenge

You will receive an array as a parameter that contains 1 or more integers and a number `n`

.

Here is a little visualization of the process:

- Step 1: Split the array in two:
`[1, 2, 5, 7, 2, 3, 5, 7, 8] / \ [1, 2, 5, 7] [2, 3, 5, 7, 8]`

- Step 2: Put the arrays on top of each other:
`[1, 2, 5, 7] [2, 3, 5, 7, 8]`

- Step 3: Add them together:
`[2, 4, 7, 12, 15]`

Repeat the above steps `n`

times or until there is only one number left, and then return the array.

**Example**s

```
Input: arr=[4, 2, 5, 3, 2, 5, 7], n=2
Round 1
-------
step 1: [4, 2, 5] [3, 2, 5, 7]
step 2: [4, 2, 5]
[3, 2, 5, 7]
step 3: [3, 6, 7, 12]
Round 2
-------
step 1: [3, 6] [7, 12]
step 2: [3, 6]
[7, 12]
step 3: [10, 18]
Result: [10, 18]
```

## The solution in Java code

Option 1:

```
import static java.util.Arrays.copyOfRange;
class Solution {
static int[] splitAndAdd(int[] numbers, int n) {
if (numbers.length > 1 && n > 0) {
int[] half = copyOfRange(numbers, numbers.length / 2, numbers.length);
for (int i = 0; i < numbers.length / 2; i++) {
half[numbers.length % 2 > 0 ? i + 1 : i] += numbers[i];
}
return splitAndAdd(half, n - 1);
}
return numbers;
}
}
```

Option 2:

```
public class Solution {
public static int[] splitAndAdd(int[] arr, int n) {
if (n<=0 || arr.length==1) return arr;
int len = arr.length/2;
int[] arr1 = new int[len], arr2 = new int[arr.length-len];
System.arraycopy(arr, 0, arr1, 0, len);
System.arraycopy(arr, len, arr2, 0, arr.length-len);
int i = arr2.length - arr1.length;
for (int a:arr1) arr2[i++] += a;
return splitAndAdd(arr2, n-1);
}
}
```

Option 3:

```
public class Solution {
public static int[] splitAndAdd(int[] numbers, int n) {
if (n == 0) return numbers;
final int len = numbers.length;
final int next[] = new int[(len+1)/2];
for (int i = 0; i < next.length; i++) next[i] += numbers[len/2+i];
for (int i = len/2-1, j=next.length-1; i >= 0; i--,j--) next[j] += numbers[i];
return splitAndAdd(next, n-1);
}
}
```

## Test cases to validate our solution

```
import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;
import java.util.*;
public class TestClass {
@Test
public void splitAndAdd() throws Exception {
int[] expected = new int[]{5,10};
int[] input = Solution.splitAndAdd(new int[]{1,2,3,4,5},2);
assertEquals(Arrays.toString(expected), Arrays.toString(input));
expected = new int[]{15};
input = Solution.splitAndAdd(new int[]{1,2,3,4,5},3);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
expected = new int[]{15};
input = Solution.splitAndAdd(new int[]{15},3);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
expected = new int[]{183, 125};
input = Solution.splitAndAdd(new int[]{32,45,43,23,54,23,54,34},2);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
expected = new int[]{32,45,43,23,54,23,54,34};
input = Solution.splitAndAdd(new int[]{32,45,43,23,54,23,54,34},0);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
expected = new int[]{305, 1195};
input = Solution.splitAndAdd(new int[]{3,234,25,345,45,34,234,235,345},3);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
expected = new int[]{1040, 7712};
input = Solution.splitAndAdd(new int[]{3,234,25,345,45,34,234,235,345,34,534,45,645,645,645,4656,45,3},4);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
expected = new int[]{79327};
input = Solution.splitAndAdd(new int[]{23,345,345,345,34536,567,568,6,34536,54,7546,456},20);
assertEquals(Arrays.toString(expected),Arrays.toString(input));
}
}
```