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

title

title
Sum All Odd Fibonacci Numbers

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

Problem Explanation:

You will need to gather all the Fibonacci numbers and then check for the odd ones. Once you get the odd ones then you will add them all. The last number should be the number given as a parameter if it actually happens to be an off Fibonacci number.

Relevant Links

• Fibonacci number

Hint: 1

To get the next number of the series, you need to add the current one to the previous and that will give you the next one.

try to solve the problem now

Hint: 2

To check if a number is even all you have to check is if number % 2 == 0.

try to solve the problem now

Hint: 3

As you get the next odd one, don't forget to add it to a global variable that can be returned at the end. result += currNumber; will do the trick.

try to solve the problem now

Spoiler Alert!

Solution ahead!

Basic Code Solution:

function sumFibs(num) {
    var prevNumber = 0;
    var currNumber = 1;
    var result = 0;
    while (currNumber <= num) {
        if (currNumber % 2 !== 0) {
            result += currNumber;
        }

        currNumber += prevNumber;
        prevNumber = currNumber - prevNumber;
    }

    return result;
}

// test here
sumFibs(4);

Run Code

Code Explanation:

• Create a variable to keep record of the current and previous numbers along with the result that will be returned.
• Use a while loop to make sure we do not go over the number given as parameter.
• We use the modulo operand to check if the current number is odd or even. If it is even, add it to the result.
• Complete the Fibonacci circle by rotating getting the next number and swapping values after.
• Return the result.

Relevant Links

• JS while Loop

Intermediate Code Solution:

function sumFibs(num) {
    // Perform checks for the validity of the input
    if (num < 0) return -1;
    if (num === 0 || num === 1) return 1;

    // Create an array of fib numbers till num
    const arrFib = [1, 1];
    let nextFib = 0;

    // We put the new Fibonacci numbers to the front so we
    // don't need to calculate the length of the array on each
    // iteration
    while((nextFib = arrFib[0] + arrFib[1]) <= num) {
        arrFib.unshift(nextFib);
    }

    // We filter the array to get the odd numbers and reduce them to get their sum.
    return arrFib.filter(x => x % 2 != 0).reduce((a, b) => a + b);
}

// test here
sumFibs(4);

Run Code

Code Explanation:

• Create an array of fibonacci numbers till num.
• Use filter() method to filter out even numbers.
• Use reduce() method to sum the remaining (odd) values.
• Return the sum.

Relevant Links

• JS Array Prototype Push
• JS For Loops Explained
• JS Array Prototype Filter
• JS Array Prototype Reduce

NOTES FOR CONTRIBUTIONS:

• DO NOT add solutions that are similar to any existing solutions. If you think it is similar but better, then try to merge (or replace) the existing similar solution.
• Add an explanation of your solution.
• Categorize the solution in one of the following categories — Basic, Intermediate and Advanced.