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javascriptfibonacci
FeCH
FeCH

Reputation: 133

Project Euler #2, Fibonacci, javascript attemp

I was attempting to do some problems on project euler. For the second one I did get the correct answer but I cheated a bit.

Heres the problem:

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

Heres my code:

var fib = [1,2];
var i = 0;
var sum = 0;
while (fib[0] + fib[1] < 4000000){
    i = fib[0] + fib[1];
    console.log(i); //just to show myself the number came out correctly.
    fib[0] = fib[1];
    fib[1] = i;

    if (i % 2 === 0){
        sum += i;
    }
}
console.log(sum + 2);

I added sum by 2 because I can't figure a way for the code to add the initial fib[1], which is a even number itself. Thanks.

Upvotes: 0

Views: 2448

Answers (6)

Nihilistic Hare
Nihilistic Hare

Reputation: 1

function firstNofFibonacci(n)
{
    let fibArr = [];
    for (let i = 0; i < n; i++) {
        if (fibArr.length > 1) {
            fibArr.push(fibArr[fibArr.length - 1] + 
                fibArr[fibArr.length - 2]);
        } else {
            fibArr.push(i);
        };
    };
    return fibArr;
}

Upvotes: 0

beingrahuul
beingrahuul

Reputation: 31

let num1 = 0; 
let num2 = 1;
let total = 0;
let num3 = 0;
let i = 0;
while(num1 + num2 < 4000000){
     num3 = num1 + num2;
     num1 = num2; //as loop keep going is changes the position of number
     num2 = num3; //as loop keep going is changes the position of number
     if(num3 % 2 === 0 ){ // check weather number is even or not 
        total += num3;    //every even number gets added
        }
     i++
}
console.log(total);

Upvotes: 0

krolovolk
krolovolk

Reputation: 472

Simple solution

var sum = 0;
var term1 = 1;
var term2 = 1;

while (term2 < 4000000) {
    term2 = term1 + term2;
    term1 = term2 - term1;
    sum += term2 % 2 === 0 ? term2 : 0;
}
console.log(sum);

Upvotes: 2

Roberto Carlos Ocampo Millan
Roberto Carlos Ocampo Millan

Reputation: 1

This is my code for the same problem. It is not perfect but I hope this will help someone who reads this.

function fibonacci(stop) {
  var a = 1, b = 0, c, storage = []
  for (var i = 0; a < stop; i++) {
    c = a
    a = a + b
    b = c
    if (b%2 == 0) {
      let even = b
      storage.unshift(even)
    }
  }
  var all = storage.reduce((x, y) => {return x + y}, 0)
  console.log(all)
}

fibonacci(4000000); // 4613732

well, what I did here is that I create a function with the stop parameter (where you tell the function to stop) and then I create variables to make the Fibonacci sequence and create a variable where I can store the even values. Then push all the even values in the array, at the end of the function I add all the values in a variable and console.log() the value

If you have suggestions or comments all ears :)

Upvotes: -1

meteorx
meteorx

Reputation: 19

for (var sum = 0, i = 0, j = 0, k = 1; 4e6 > j + k; i++) i = j + k, j = k, k = i, sum += 0 == i % 2 ? i : 0;

It could help you.

Upvotes: 0

Jean-Alphonse
Jean-Alphonse

Reputation: 816

If you start with [1, 2], the first fibonacci number that you get is 3.

In your loop you have: 

i = 1+2 = 3
i = 2+3 = 5

So simply start with [0, 1]: 

i = 0+1 = 1
i = 1+1 = 2
i = 1+2 = 3

Fixed code:

var fib = [0,1];
var i = 0;
var sum = 0;
while (fib[0]+fib[1] < 4000000){
    i= fib[0]+fib[1];
    fib[0]=fib[1];
    fib[1]=i;

        if(i%2 === 0){
        sum += i;
    }
}
console.log(sum);

Upvotes: 1

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