Project Euler #2

euler2.js

// 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.

// function makeFibsArray (howManyFibs) {
//   var fibsArray = [1,2];
//   for (var i = fibsArray.length - 1; i<=howManyFibs; i++) {
//     fibsArray.push(findNextFibInArray(fibsArray));
//   }
//   return fibsArray;
// }

function findNextFibInArray (array) {
  return (array[array.length-2] + array[array.length-1]);
}

function makeFibsArrayUnder(topFib) {
  var fibsArray = [1,2];
  for (var i = fibsArray.length - 1; fibsArray[i]<topFib; i++) {
    fibsArray.push(findNextFibInArray(fibsArray.slice([fibsArray.length, fibsArray.length+1])));
  }
  return fibsArray;
}

function addUpEvensInArray (array) {
  var total = 0;
  for (var i = array.length - 1; i >= 0; i--) {
    if (array[i] % 2 === 0) {
      total += array[i];
    }
  }
  return total;
}

function solve () {
  return addUpEvensInArray(makeFibsArrayUnder(4000000));
}