# Sum All Numbers in a Range

## Problem Explanation

You need to create a program that will take an array of two numbers who are not necessarily in order, and then add not just those numbers but any numbers in between. For example, [3,1] will be the same as `1+2+3`

and not just `3+1`

## Hints

### Hint 1

Use `Math.max()`

to find the maximum value of two numbers.

### Hint 2

Use `Math.min()`

to find the minimum value of two numbers.

### Hint 3

Remember to that you must add all the numbers in between so this would require a way to get those numbers.

## Solutions

## Solution 1 (Click to Show/Hide)

```
function sumAll(arr) {
var max = Math.max(arr[0], arr[1]);
var min = Math.min(arr[0], arr[1]);
var temp = 0;
for (var i = min; i <= max; i++) {
temp += i;
}
return temp;
}
sumAll([1, 4]);
```

#### Code Explanation

- First create a variable to store the max number between two.
- The same as before for the Smallest number.
- We create a temporary variable to add the numbers.

Since the numbers might not be always in order, using `max()`

and `min()`

will help organize.

#### Relevant Links

## Solution 2 (Click to Show/Hide)

```
const sumAll = arr => {
// Buckle up everything to one!
const startNum = arr[0];
const endNum = arr[1];
// Get the count of numbers between the two numbers by subtracting them and add 1 to the absolute value.
// ex. There are |1-4| + 1 = 4, (1, 2, 3, 4), 4 numbers between 1 and 4.
const numCount = Math.abs(startNum - endNum) + 1;
// Using Arithmetic Progression summing formula
const sum = ((startNum + endNum) * numCount) / 2;
return sum;
};
```

#### Code Explanation

- The formula for calculating the sum of a continuous range is â(startNum + endNum) * numCount / 2â.
- arr[0] and arr[1] can either be startNum or endNum, order doesnât matter.
- We can get the count of numbers in range by âMath.abs(arr[0] - arr[1]) + 1â.
- Applying the formula by plugging in the numbers.

#### Relevant Links

## Solution 3 (Click to Show/Hide)

```
function sumAll(arr) {
var sum = 0;
for (var i = Math.min(...arr); i <= Math.max(...arr); i++) {
sum += i;
}
return sum;
}
sumAll([1, 4]);
```

#### Code Explanation

- Creating a variable sum to store the sum of the elements.
- Starting iteration of the loop from min element of given array and stopping when it reaches the max element.
- Using a spread operator (âŚarr) allows passing the actual array to the function instead of one-by-one elements.

#### Relevant Links

## Solution 4 (Click to Show/Hide)

**Recursive Solution**

```
function sumAll([ first, last ] ) {
const step = first - last < 0 ? 1 : -1;
return first !== last
? first + sumAll([ first + step, last ])
: first;
}
```