How to check if a number is a fibonacci number?

Question

Im trying to create a function that determines if a number is a fibonacci number or not in Scala. Can someone look at my code and let me know what I'm missing? Thanks

def isFibNumber(n: Int): Boolean = {

  var fib1 = 0;
  var  fib2 = 1;
do {
    var saveFib1 = fib1;
    fib1 = fib2;
    fib2 = saveFib1 + fib2;
    }
while (fib2 < n);

if (fib2 == n)
    return true;
else
    return false;
}

For alternative solutions see http://stackoverflow.com/questions/2432669/test-if-a-number-is-fibonacci — Thilo, Feb 04 '16 at 03:56

Sibidharan · Answer 1 · 2016-02-08T07:22:20.593

2

def isFibonacciNumber(n: Int): Boolean = {
  var fib1 = -1;
  var  fib2 = 1;
  var res = 0;

do {
    res = fib1+fib2;
    fib1 = fib2;
    fib2 = res;
} while (res < n);

if (res == n)
    return true;
else
    return false;
}

This should work. You had error in your algorithm.

edited Feb 08 '16 at 07:22

answered Feb 04 '16 at 03:55

Sibidharan

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Did you test your code? it doesnt seem to be working. Also as part of the requeriment of this task I need to use def isFibNumber(n: Int): Boolean = { and not def firstNFibonacciNumbers(n: Int): Stream[Int] = { – abpre Feb 04 '16 at 04:03
@abpre can u be more presice? So I can help you. – Sibidharan Feb 08 '16 at 07:20

jdevelop · Accepted Answer · 2016-02-04T04:10:58.673

2

That would help. No loop required

http://www.geeksforgeeks.org/check-number-fibonacci-number/

object Fib {


  def isPerfectSq(n: Int): Boolean = {
    val res = math.round(math.sqrt(n))
    res * res == n.toLong
  }

  def isFibonacci(n: Int) = {
    isPerfectSq(5 * n * n - 4) || isPerfectSq(5 * n * n + 4)
  }


}

edited Feb 04 '16 at 04:10

answered Feb 04 '16 at 04:06

jdevelop

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Thanks for your answer! – abpre Feb 04 '16 at 04:32
Hmmm... is it getting in some strange overflow issues? `isFibonacci(fib(29))` returns false. Same for others higher. I feel it hits an Int limitation right around there. – marios Feb 04 '16 at 05:14
Perhaps you might want to use Long, or even BigInt – jdevelop Feb 04 '16 at 17:14

How to check if a number is a fibonacci number?

2 Answers2