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javascriptfor-loopfibonacci
Alex Legault
Alex Legault

Reputation: 61

Javascript Euler Fibonacci for loop

I'm doing the Euler project problem 2 in which the objective is to sum the even numbers of the fibonacci sequence that have a value of less than 4 million. I've searched a bit and I've seen several solutions using a while loop but nothing simple using a for loop. I'm curious why I'm returning zero with the following code:

var array = [];
array[0] = 0;
array[1] = 1;

var total = 0;

for(var i=2;total<=4000000;i++) {
array[i] = array[i-1] + array[i-2];};


for(var x=0;x<array.length;x++){
if(array[x]%2 === 0){
total += array[x]};};

alert(total);

I'm guessing the problem is in my for loop using the total variable. I couldn't get it to work using array[i]<=4000000 either and I'm really curious behind the why here. Anyone know why this is? What can I change in the for loop condition (second statement) to get a correct total here?

Upvotes: 0

Views: 1112

Answers (3)

Cem &#214;zer
Cem &#214;zer

Reputation: 1283

First of all there is an infinite loop at first for. Your condition must be array[i-1] < 4000000. After that your second for loop will find the correct result.

Also for the problem, you don't need to store all fibonacci numbers then find sum of even numbers. You can calculate sum when calculating fibonacci.

var first = 0;
var second = 1;
var sum = 0;

for(var current=first+second; current < 4000000; current = first+second){
    if(current%2 === 0){
        sum+=current;
    }
    first = second;
    second = current;
}

Upvotes: 1

Nicola Avancini
Nicola Avancini

Reputation: 26

Sorry but for me your code going in a dead loop. first "for" use total as check but it's never incremented. If you want This is a solution for fibonacci sequence based on dinamic programming with memoization tecnic. 

var f1 = 1;
 var f2 = 1;

 for(var i = 2; i < 40000; i++){
  console.info(i, f1, f2);
  var temp = f1 + f2;
  f1 = f2;
  f2 = temp;
 }

 alert(f2);

Upvotes: 0

pid
pid

Reputation: 11607

I fixed it for you.

var i, data = [ 0, 1 ], total = 0;

for (i = 2; i <= 4000000; i++)
{
    data[i] = data[i - 1] + data[i - 2];

    if (data[i] % 2 === 0)
    {
        total += data[i];
    }
}

alert(total);

I'm not sure what you termination condition should be like, you say have a value of less than 4 million, but this is ambiguous. Maybe it should be total <= 4000000 or data[i] <= 4000000. Your phrasing is not precise enough.

Upvotes: 1

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