# Calculate the Sum without highest and lowest number in Java

## The challenge

Sum all the numbers of the array except the highest and the lowest element (the value, not the index!).
(The highest/lowest element is respectively only one element at each edge, even if there are more than one with the same value!)

Example:

```{ 6, 2, 1, 8, 10 } => 16
{ 1, 1, 11, 2, 3 } => 6
```

If array is empty, null or None, or if only 1 Element exists, return 0.

## The solution in Java code

Option 1 (first pass):

```public class Solution {
public static int sum(int[] numbers) {
// catch some edge cases
if (numbers==null || numbers.length<3) return 0;

// sort the array
java.util.Arrays.sort(numbers);

// sum up elements excluding the first and last
int sum = 0;
for(int i=1;i<numbers.length-1;i++) {
sum += numbers[i];
}
return sum;
}
}
```

Option 2 (using `IntStream`):

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

public class Solution {
public static int sum(int[] numbers) {
return (numbers == null || numbers.length <= 2) ? 0 : of(numbers).sum() - of(numbers).max().getAsInt() - of(numbers).min().getAsInt();
}
}
```

Option 3 (using `streams`):

```import java.util.Arrays;

public class Solution {
public static int sum(int[] numbers) {
if(numbers == null || numbers.length < 2) return 0;
Arrays.sort(numbers);
return Arrays.stream(numbers).skip(1).limit(numbers.length-2).sum();
}
}
```

## Test cases to validate our code solution

```import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;

public class SolutionTest {
@Test
public void BasicTests() {
assertEquals(16, Solution.sum(new int[] { 6, 2, 1, 8, 10}));
}
}
```

## More extensive test cases to catch edge-cases

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

public class SolutionTest {
@Test
public void SumOnlyOneElement() {
assertEquals(0, Solution.sum(new int[] { 6 }));
}

@Test
public void SumOnlyTwoElements() {
assertEquals(0, Solution.sum(new int[] { 6, 7 }));
}

@Test
public void SumPositives() {
assertEquals(16, Solution.sum(new int[] { 6, 2, 1, 8, 10 }));
}

@Test
public void SumPositivesWithDoubleMax() {
assertEquals(17, Solution.sum(new int[] { 6, 0, 1, 10, 10 }));
}

@Test
public void SumNegatives() {
assertEquals(-28, Solution.sum(new int[] { -6, -20, -1, -10, -12}));
}

@Test
public void SumMixed() {
assertEquals(3, Solution.sum(new int[] { -6, 20, -1, 10, -12}));
}

@Test
public void SumEmptyArray() {
assertEquals(0, Solution.sum(new int[0]));
}

@Test
public void SumNullArray() {
assertEquals(0, Solution.sum(null));
}

@Test
public void SumRandom() {
for(int r=0; r<20;r++)
{
int[] numbers = new int[6];
for(int i=0; i< numbers.length; i++)
{
numbers[i] = (int)Math.floor(Math.random() * 1100 - 500);
}

int sum = 0;
for(int i = 0 ; i < numbers.length; i++) {
sum += numbers[i];
}

int min = Arrays.stream(numbers).min().getAsInt();
int max = Arrays.stream(numbers).max().getAsInt();

int expected = sum - min - max;

assertEquals(expected, Solution.sum(numbers));
}
}
}
```
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