Sum All Numbers in a Range

The Challenge:

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.

My Solution:

While the explanation is light, I feel the solution will be quite a hefty task! I first want to avoid that little caveat that “the lowest number will not always come first” so I’ll use a simple if statement to swap the numbers if they do not appear in the array in order.

Since I feel it will help me think more clearly, I will set arr[0] to a and arr[1] to b.

Next I want to somehow create an array containing the value of a at [0] and then every integer up until the value of b. The length of the array would be determined by calculating b - a. I want to try to do this with map(), but I’m not sure that would work since I have only seen map() used to output an array of the same size as the one that is fed in.

I went with a bloody for loop again. I must try and break out of this loop of using for loops…

  let count = 0;

  for(let i=0; i<=arrLen; i++) {
    newArr.push(a+count);
    count++
  } 

This creates the array I need. So if a = 1 and b = 5, I will get an array of [1,2,3,4,5]. What I’m going to attempt to do next is use the reduce() method to smoosh these numbers together.

And that seems to work!

function sumAll(arr) {

  //ensure that array numbers are always in order

  let a = arr[0];
  let b = arr[1];

  if(arr[0]>arr[1]){
    b = arr[0];
    a = arr[1];
  } 

  //next create an empty array

  let newArr = [];

  const arrLen = b - a; //length of new array

  let count = 0; 

  //map all relevant integers to new array

  for(let i=0; i<=arrLen; i++) {
    newArr.push(a+count);
    count++
  }

  //reduce array to sum of all numbers

  const result = newArr.reduce((total,num)=>total+num);

  return result;

}

sumAll([10, 5]);

Let’s have a look at the FCC solution to see how the pros do it!

Okay so for the first part where I use a conditional to swap the integers if they were not in order, they suggest using Math.max() and/or Math.min() to determine the relative size of the integers. Oh…. oh…! The whole stage where I created a new array of integers was totally unnecessary. They also used a for loop, but they used it to add the values directly. Here is the FCC solution:

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]);