Project Euler - Proble #1 Solution

Problem

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Problem Description

This is a more straightforward problem.

The natural numbers below 10 would be 1,2,3,4,5,6,7,8 and 9 (Since it is below 10, 10 is exclusive)

And those multiples of 3 are 3, 6 and 9

And multiples of 5 would be 5.

So now, the sum of all those multiples would be,

3 + 6 + 9 + 5 = 23.

So now, we want to find the sum of all the multiples of 3 and 5 below 1000 (1000 is exclusive)

Approach

My approach is to get all the multiples of 3 or 5 in an array - multiples and then use Array.prototype.reduce() function to calculate the sum of all items in that array multiples

For my solution, the time taken is between 0.11ms and 0.14ms.

Another approach can be to add the multiples directly to a variable, instead of pushing to an array. Inside the if, we can use sum += i and print the sum which is our result.

As I said before, there is more than one approach to each problem!

Solution

const multiples = [];

for (let i = 1; i < 1000; i++) {
    if (i % 3 === 0 || i % 5 === 0) {
        multiples.push(i);
    }
}

console.time("p#1");
console.log(multiples.reduce((acc, curVal) => acc + curVal));
console.timeEnd("p#1");

Project Euler: #1 Solution Answer

The GitHub repo for this problem is found at 01

If you have another solution, please leave it in the comments below.

For the other Project Euler Solutions, please follow the series Project Euler Solutions in JS.

Thank you!

Project Euler: #1 - Multiples of 3 or 5

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