Creating a function that provides the greatest Fibonacci number that is less than or equal to 'n'?

Question

I am trying to create a function that takes an input 'n' and provides an output which is the highest Fibonacci number that's less than or equal to 'n'. For example, if n = 5, then output is 5. If n = 6, then output is 5.

My solution is workable but it does not seem "efficient" and I am looking for an alternative method. Here is what I did:

def fib(n):

    if n<0:
        print("Invalid input")
    x , y = 0 , 1
    while x <= n:
        x , y = y , y + x
    return abs(x-y)

I don't think that using abs(x-y) seems very efficient so I would like to ask if anybody has a different way to solving this problem. Thank you.

You'd be hard pressed to find a non-trivial function that's more efficient than `abs`. — mypetlion, Jul 10 '18 at 20:52
SInce `y` will always be greater than `x`, it's more efficient to not use `abs` at all. — Jan Christoph Terasa, Jul 10 '18 at 20:55
Why don't you compare against y, then return x? At any rate, I don't think you'll get much more faster than you already are without switching to another language. — Ben Jones, Jul 10 '18 at 21:02
You might want to use a callable object. Then it is quite easy to store the the fibonacci number you have generated in a cache. Then you won't need to generate them over and over again. Only when you specify a number greater than you have ever used before. — hetepeperfan, Jul 10 '18 at 21:12

score 0 · Answer 1 · answered Jul 10 '18 at 20:53

0

def fib(n):
    if n<0:
        print("Invalid input")
    x , y = 0 , 1
    while x <= n:
        x , y = y , y + x
    return y - x

answered Jul 10 '18 at 20:53

Jan Christoph Terasa

5,781
24
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score 0 · Answer 2 · answered Jul 11 '18 at 09:57

0

This Solution for your question

def fib(n):
    x, y = 0, 1
    while True:
        x, y = y , x + y
        if x > n:
            return y-x

with this you get correct answer

answered Jul 11 '18 at 09:57

Om trivedi

32
3

Creating a function that provides the greatest Fibonacci number that is less than or equal to 'n'?

2 Answers2