Sum All Numbers in a Range

DESCRIPTION:

We'll pass you an array of two numbers. Return the sum of those two numbers plus the sum of all the numbers between them. The lowest number will not always come first.

Examples

sumAll([1, 4]) `should return 10`.

sumAll([10, 5]) `should return 45`.

My approach for solving this problem:

• find the min and max value in the array.
• fill the array with range from min to max.
• if not return sliced str with num length.
• get the summation of the array with reduce().

My solution:

function sumAll(arr) {
  const minNumber = Math.min(...arr);
  const maxNumber = Math.max(...arr);
  return new Array(maxNumber - minNumber + 1)
  .fill()
  .map((num,index)=> minNumber+index)
  .reduce((perv,num) => perv + num)
}

sumAll([1, 4]);

Any tips or edit are most welcome. share it with me on the comments. Thanks for being here!

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Comments

[Jon Randy 🎖️]

My approach, based on the fact that the sum from 0→n is equal to (n/2)(n+1):

const sumAll =
  (arr, [a,b]=[...arr].sort((c,d)=>c-d))=>(b*b-a*a+b+a)/2

(Could be made shorter by not copying the original array, but I wanted to avoid mutation)

[Jon Randy 🎖️]

With mutation (and more code golf):

const sumAll=(a,[b,c]=a.sort((d,e)=>d-e))=>(c*c-b*b+c+b)/2

[Mohammed Awad]

thank you, Relly for your interest!

[donnywi]

This works fast too when you pass in:
sumAll(7, 80000)

function sumAll(arr) {
    return ( (arr[0]+arr[1]) * (Math.abs(arr[0]-arr[1])+1) ) /2 ;
}

[Mohammed Awad]

I'm suck at Math; I hope to be become good like that someday.

[donnywi]

I think you're awesome at Javascript, and I need to learn how to use fill(), map(), and reduce() properly. I'm new at Javascript, so your posts are very inspiring.

[Mohammed Awad]

Relly, glad to hear that. you can check freecodecamp.com to learn more

[Red Ochsenbein (he/him)]

Try and be amazed:

function sumAll(arr) {
  const minNumber = Math.min(...arr);
  const maxNumber = Math.max(...arr);
  return (maxNumber*(maxNumber+1)/2) - ((minNumber-1)*minNumber/2);
}

[Mohammed Awad]

this is a pattern ?

[donnywi]

I belive that's just a basic math equation.

[Mohammed Awad]

Yeah, but I mean is it design pattern.

[Red Ochsenbein (he/him)]

Nah. It's math. The basic idea is that you can calculate the sum of all integers from 1 to n using n*(n+1)/2

[Mohammed Awad]

I need to focus on math and learn how use it because better with BigO

[Red Ochsenbein (he/him)]

I'm not very good at math. I just happen to know some of the more usual stuff like exactly this one.

[Andrew Bone]

function sumAll(arr) {
  const [a, l] = arr.sort((a, b) => a - b);

  return (l - a + 1) * (a + l) / 2;
}

[Mohammed Awad]

Any tips or edit are most welcome. share it with me on the comments. Thanks for being here!

[Jon Randy 🎖️]

Another one (no mutation):

const sumAll = ([m,n],[a,b]=m>n?[n,m]:[m,n])=>(b*b-a*a+b+a)/2

[Mohammed Awad]

great but it's seemed little complex, right? I more into simple solutions

[Jon Randy 🎖️]

It's interesting you would say that, as your solution is actually the most complex (timewise) here at O(N). The simplest I can now think of is a small reworking of @donnywi solution (which in itself is a slight mathematical simplification of others here):

const sumAll = ([a, b]) => (a+b) * (Math.abs(a-b)+1) / 2 

[Jon Randy 🎖️]

I suspect the way I wrote my code in posts here may have made it look more complex than it is, as it doesn't really explain itself. Sorry, my brain often tends to work in terse, code-golf like code.

[Mohammed Awad]

yes, I know my code was the worst, but it easier to read than yours, I should study the math section again, because I didn't Relly use Math methods expect min, max and random.

[donnywi]

This is a good use of the arrow function. 👍