freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/sum-all-numbers-in-a-range/index.md

title
Sum All Numbers in a Range

Remember to use Read-Search-Ask if you get stuck. Try to pair program and write your own code

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

Hint: 1

Use Math.max() to find the maximum value of two numbers.

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Hint: 2

Use Math.min() to find the minimum value of two numbers.

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Hint: 3

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

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Spoiler Alert!

Solution ahead!

Basic Code 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]);

Run Code

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

• Math.max()
• Math.min()
• For Loops

Intermediate Code Solution:

function sumAll(arr) {
  // Buckle up everything to one!

  // Using ES6 arrow function (one-liner)
  var sortedArr = arr.sort((a,b) => a-b);
  var firstNum = arr[0];
  var lastNum = arr[1];
  // Using Arithmetic Progression summing formula

  var sum = (lastNum - firstNum + 1) * (firstNum + lastNum) / 2;
  return sum;
}

Run Code

Code Explanation:

• Firstly, we create a variable called sortedArr which sorts it from the lowest to the highest value.
• firstNum is equal to the first number and lastNum is equal to the second number.
• Next, using the Arithmetic Progression summing formula we let sum equal (lastNum - firstNum + 1) * (firstNum + lastNum) / 2.
• Finally, we return sum.

The line var sortedArr = arr.sort((a,b) => a-b); is probably what will have you more confused. This would be the same as creating a function that returns a-b for the sort() which is the standard way to sort numbers from smallest to largest. Instead using arrow or fat arrow function, we are able to do all that in one single line thus allowing us to write less.

Relevant Links

• Array.sort()
• Arithmetic Progression summing formula
• ES6 arrow function

Advanced Code Solution:

function sumAll(arr) {
    var sum = 0;
    for (var i = Math.min(...arr); i <= Math.max(...arr); i++){
        sum += i;
    }
  return sum;
}

sumAll([1, 4]);

Run Code

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 (...arr) allows passing the actual array to the function instead of one-by-one elements.

Relevant Links

• Spread Operator
• Using Spread Operator in Math.max()

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