CODEWITHSUNDEEP
pythonfibonacci
nisa
nisa

Reputation: 43

Find the nth number of fibonacci sequence

I have this code, with input_number = 10. I have to make a fibonacci sequence with condition: fibo[-2] < input_number < fibo[-1]

def fibonacci(input_number):
  a = 0
  b = 1
  fibo=[a, b]
  while b < input_number:
    a, b = b, a+b
    fibo.append(b)
    print(fibo)

and the output was like this, just as I expected:

[0, 1, 1]
[0, 1, 1, 2]
[0, 1, 1, 2, 3]
[0, 1, 1, 2, 3, 5]
[0, 1, 1, 2, 3, 5, 8]
[0, 1, 1, 2, 3, 5, 8, 13]

But the problem now is that I want to call the last fibonacci number which is 13 and the output supposed to be "The last fibonacci number is 13 and it is the 8th fibonacci number". But I can't call the number of 13 because it is an integer and not a list.

How can I convert that into a list?

Upvotes: 1

Views: 1023

Answers (3)

Saadat Ahmed
Saadat Ahmed

Reputation: 1

All the previous codes have a greater time complexity.

However, there is a separate way of doing it in constant time, if we consider the pow() or ** and sqrt() function to work in constant time.

Considering the series to be in the following format => 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...

Where,
0 ----> 0 th fibonacci number
1 ----> 1 th fibonacci number
1 ----> 2 th fibonacci number
2 ----> 3 rd fibonacci number
3 ----> 4 th fibonacci number
5 ----> 5 th fibonacci number

The mathematical formula to calculate the nth Fibonacci number in a constant time/O(1) is:

enter image description here

The python code should be something like this:

from math import sqrt

# n defines the nth fibonacci number
n = 5

def fib(n):
    p = ( 1 + sqrt(5) ) / 2
    q = ( 1 - sqrt(5) ) / 2
    return int((p**n-q**n) / sqrt(5)) 
    # to counter float value from the division operator int is used

print(fib(n))

Input:

5

Output:

5

Upvotes: 0

Jagrut Sharma
Jagrut Sharma

Reputation: 4754

You probably just need the syntax to access the fibo array. Hope the below helps:

def fibonacci(input_number):
    a = 0
    b = 1
    fibo = [a, b]
    while b < input_number:
        a, b = b, a + b
        fibo.append(b)
        print(fibo)

    print(f'fibonacci number {len(fibo)} is {fibo[len(fibo) - 1]}')
    print('===')
    i = 0
    while i < len(fibo):
       print(f'fibonacci number {i + 1} is {fibo[i]}')
       i += 1

fibonacci(10)

Result:

[0, 1, 1]
[0, 1, 1, 2]
[0, 1, 1, 2, 3]
[0, 1, 1, 2, 3, 5]
[0, 1, 1, 2, 3, 5, 8]
[0, 1, 1, 2, 3, 5, 8, 13]
fibonacci number 8 is 13
===
fibonacci number 1 is 0
fibonacci number 2 is 1
fibonacci number 3 is 1
fibonacci number 4 is 2
fibonacci number 5 is 3
fibonacci number 6 is 5
fibonacci number 7 is 8
fibonacci number 8 is 13

Upvotes: 0

Tom Gionfriddo
Tom Gionfriddo

Reputation: 430

fibo is the list containing all of your values. To get the last value of the list you can index it by -1, so fibo[-1]. We can then determine which Fibonacci number fibo[-1] is by getting the length of the list, len(fibo).

I wont write the full answer for you, but put this

print("fibo[-1]==",fibo[-1], " len(fibo)==", len(fibo))

outside the while loop, and I think you'll be able to figure it out from there.

Upvotes: 0

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