First 30 numbers of the fibonacci sequence with arrays

Question

so I have to make a thing for school, but I can't figure it out. So I have to get the first 30 numbers of the Fibonacci sequence using arrays. The code should be simple, and mine looks something like this.

fib = [0, 1] * 15
for i in range(30):
    fib = fib[i-1] + fib[i-2]
    print(fib)

Any input is appreciated!

@trincot "avoid negative indexes". Why? Negative indexing is a very strong and useful feature for accessing Python lists — DarkKnight, Mar 18 '22 at 07:10
Honestly for the first 30 I'd use the naive recursive exponential time solution without any optimization, just to annoy the instructor :-D. Takes less than a second, so they can't complain. — Kelly Bundy, Mar 18 '22 at 07:22

score 0 · Accepted Answer · answered Mar 18 '22 at 06:52

0

What you have is fairly close with some modification, that is, the Fibonacci sequence starts with 1, 1 not 0, 1 and you need to store the result of each calculation for the next:

fib = [1]*30
for i in range(2, 30):
    fib[i] = fib[i-1] + fib[i-2]
    print(fib[i])

answered Mar 18 '22 at 06:52

wogsland

9,106
19
57
93

Then why does Wikipedia say ["The sequence commonly starts from 0 and 1"](https://en.wikipedia.org/wiki/Fibonacci_number)? – Kelly Bundy Mar 18 '22 at 07:12
Why does [OEIS](http://oeis.org/search?q=fibonacci&sort=&language=&go=Search) show it starting with 0, 1? – Kelly Bundy Mar 18 '22 at 07:14
[WolframAlpha](https://www.wolframalpha.com/input?i=fibonacci+sequence) also starts it with 0, 1. How can they all be so incompetent? – Kelly Bundy Mar 18 '22 at 07:16
I've always understood that the Fibonacci sequence starts with zero. You live and learn – DarkKnight Mar 18 '22 at 07:17
Why does this code emit 2 as the first value in the sequence? (rhetorical) – DarkKnight Mar 18 '22 at 07:36

DarkKnight · Answer 2 · 2022-03-18T07:39:09.570

0

A generator is ideal for this exercise.

Try this:

def fibonacci(n):
    a = 0
    b = 1
    for _ in range(n):
        yield a
        a, b = b, a + b

print(list(fibonacci(30)))

Output:

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811, 514229]

edited Mar 18 '22 at 07:39

answered Mar 18 '22 at 07:15

DarkKnight

19,739
3
6
22

Jerry_V · Answer 3 · 2022-03-20T08:00:20.690

I think you can just use this:

fib = [0, 1]
for i in range(1,30):
    fib.append(fib[i] + fib[i-1])
print(fib)

The changes I have made is to append each fib number to the list. This is important for the list to update. Before you had nothing to change or add digits to the list. Then I just took the sum of the last number on the list (fib[i] not fib[i-1]) and the same with the second to last number on the list(fib[i-1] not fib[i-2])

First 30 numbers of the fibonacci sequence with arrays

3 Answers3