Fibonacci Code Golf

Answer 1

J, 27 characters for a non-recursive function:

f=:3 :'{:}.@(,+/)^:y(0 1x)'

+/ sums over a list.
(,+/) appends the sum of a list to its tail.
}.@(,+/) sums a list, appends an element to its tail, and drops the first element.
}.@(,+/)^:y iterates the above function y times.
}.@(,+/)^:y(0 1x) applies the above function to the list (0,1) (the x makes it an integer).
{:}.@(,+/)^:y(0 1x) takes the last element of the output list of the above.
f=:3 :'{:}.@(,+/)^:y(0 1x)' defines f to be a function on one variable y.

Answer 2

For the record:

• Lua (66 chars): function f(n)if n<2 then return n else return f(n-1)+f(n-2)end end
• JavaScript (41 chars): function f(n){return n<2?n:f(n-1)+f(n-2)}
• Java (41 chars): int f(int n){return n<2?n:f(n-1)+f(n-2);}

I am not much adept of super concise languages... :-P

Chris is right, I just took the simple, recursive algorithm. Actually, the linear one is even shorter in Lua (thanks to multiple assignment)! JavaScript isn't so lucky and Java is worse, having to declare vars...

• Lua (60 chars): function f(n)a=1;b=0;for i=1,n do a,b=b,a+b end return b end
• JavaScript (60 chars): function f(n){a=1;b=i=0;for(;i++<n;){x=a+b;a=b;b=x}return b}
• Java (71 chars): int f(int n){int a=1,b=0,i=0;for(;i++<n;){int x=a+b;a=b;b=x;}return b;}

I would write Lua's code with local a,b=1,0 but it is longer, so let's pollute _G! ;-) Idem for JS.

For completeness, here are the terminal recursive versions. Lua's one, using tail call, is as fast as the linear one (but 69 chars, it is the longest!) - need to call them with three params, n,1,0.

• Lua (69 char, longer!): function f(n,a,b)if n<1 then return b else return f(n-1,b,a+b)end end
• JavaScript (44 chars): function f(n,a,b){return n<1?b:f(n-1,b,a+b)}
• Java (52 chars): int f(int n,int a,int b){return n<1?b:f(n-1,b,a+b);}

Answer 3

Befunge-93

31 chars

Will output an infinite list of the Fibonacci numbers, from 0 upwards, separated by tabs (could be reduced to 29 chars by deleting 9, in the first row, at the expense of no whitespace between numbers).

Unfortunately, all the Befunge-93 interpreters I've tried seem to overflow after 65k, so the output is only correct until and including 46368 (which is F₂₄).

#v::1p1>01g:.\:01p+9,#
 >     ^

Confirmed to work (with caveat above) with the Befunge-93 interpreter in Javascript and the Visual Befunge Applet Full.

I'm proud to say this is a completely original work (i.e. I did not copy this code from anyone), and it's much shorter than the Befunge solution currently on Rosetta Code.

Answer 4

C#

I'm seeing a lot of answers that don't actually generate the sequence, but instead give you only the fibonacci number at position *n using recursion, which when looped to generate the sequence gets increasingly slower at higher values of n.

using System;
static void Main()
{
  var x = Math.Sqrt(5);
  for (int n = 0; n < 10; n++)
    Console.WriteLine((Math.Pow((1 + x) / 2, n) - Math.Pow((1 - x) / 2, n)) / p) ;
}

Answer 5

Lua - 49 chars

function f(n)return n<2 and n or f(n-1)+f(n-2)end

Answer 6

Language: C++ Compiler Errors
Characters: 205

#define t template <int n> struct 
#define u template <> struct f
t g { int v[0]; };
t f { enum { v = f<n-1>::v + f<n-2>::v }; g<v> x;};
u<1> { enum { v = 1 }; };
u<0> { enum { v = 0 }; };
int main() { f<10> x; }