## The challenge#

### Get the averages of these numbers#

Write a method, that gets an array of integer-numbers and return an array of the averages of each integer-number and his follower, if there is one.

Example:

``````Input:  [ 1, 3, 5, 1, -10]
Output:  [ 2, 4, 3, -4.5]
``````

If the array has 0 or 1 values or is null, your method should return an empty array.

## The solution in Java code#

Option 1:

``````public class Solution {
public static double[] averages(final int[] numbers) {
final double res[] = new double[(numbers == null || numbers.length == 0) ? 0 : numbers.length - 1];
for (int i = 0; i < res.length; i++) res[i] = (numbers[i]+numbers[i+1]) / 2.0;
return res;
}
}
``````

Option 2:

``````public class Solution {
public static double[] averages(int[] numbers) {
if (numbers == null || numbers.length < 2) return new double[] {};
double [] ans = new double [numbers.length - 1];
for (int i = 0; i < ans.length; i++) ans[i] = (numbers[i] + numbers[i + 1]) / 2.0;
return ans;
}
}
``````

Option 3:

``````import java.util.stream.IntStream;

public class Solution {
public static double[] averages(int[] numbers) {
if (numbers == null || numbers.length < 2) return new double[0];
return IntStream.range(1, numbers.length)
.mapToDouble(i -> (numbers[i - 1] + numbers[i]) / 2.0)
.toArray();
}
}
``````

## Test cases to validate our solution#

``````import org.junit.Test;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertArrayEquals;
import org.junit.runners.JUnit4;
import java.util.Arrays;

public class SolutionTest {
@Test
public void basicTests() {
assertEquals(Arrays.toString(new double[] { 2, 2, 2, 2 }), Arrays.toString(Solution.averages(new int[] { 2, 2, 2, 2, 2 })));
assertEquals(Arrays.toString(new double[] { 0, 0, 0, 0 }), Arrays.toString(Solution.averages(new int[] { 2, -2, 2, -2, 2 })));
assertEquals(Arrays.toString(new double[] { 2, 4, 3, -4.5 }), Arrays.toString(Solution.averages(new int[] { 1, 3, 5, 1, -10 })));
}

@Test
public void nullEmptyTests() {
assertEquals("input 'null' should return an empty array", 0, Solution.averages(null).length);
assertEquals("Empty array as input should return an empty array", 0, Solution.averages(new int[0]).length);
assertEquals("Array with only one value as input should return an empty array", 0, Solution.averages(new int[] { 2 }).length);
}

@Test
public void randomTests() {

for(int r = 0; r < 100; r++)
{
int len = (int)Math.floor(Math.random() * 20);
int[] numbers = new int[len];
for(int k = 0; k < len; k++)
{
numbers[k] = (int)Math.floor(Math.random() * 41) - 20;
}

double[] expected = new double[0];

if(numbers.length > 1)
{
expected = new double[numbers.length - 1];
for(int i=0;i<numbers.length-1;i++)
{
expected[i] = ((double)numbers[i] + numbers[i+1]) / 2;
}
}

assertArrayEquals("Should work for random input", expected, Solution.averages(numbers), 0.001);
}
}
}
``````