# Find the Factorial!

Create the shortest program or function that finds the factorial of a non-negative integer.

The factorial, represented with ! is defined as such

$$n!:=\begin{cases}1 & n=0\\n\cdot(n-1)!&n>0\end{cases}$$

In plain English the factorial of 0 is 1 and the factorial of n, where n is larger than 0 is n times the factorial of one less than n.

Your code should perform input and output using a standard methods.

Requirements:

• Does not use any built-in libraries that can calculate the factorial (this includes any form of eval)
• Can calculate factorials for numbers up to 125
• Can calculate the factorial for the number 0 (equal to 1)
• Completes in under a minute for numbers up to 125

The shortest submission wins, in the case of a tie the answer with the most votes at the time wins.

• How many of the given answers can actually compute up to 125! without integer overflow? Wasn't that one of the requirements? Are results as exponential approximations acceptable (ie 125 ! = 1.88267718 × 10^209)?
– Ami
Commented Feb 6, 2011 at 22:43
• @SHiNKiROU, even golfscript can manage 125! less than 1/10th of a second and it's and interpreted interpreted language! Commented Feb 8, 2011 at 3:21
• Completes in under a minute seems a very hardware-dependent requirement. Completes in under a minute on what hardware? Commented Aug 24, 2017 at 18:05
• @sergiol Incredibly that hasn't been an issue in the last 2 years, I suspect most languages can get it done in under a minute. Commented Aug 24, 2017 at 21:20
• Why aren't built-ins allowed? You haven't specified what built-ins are, and if you said that it was up to a "reasonable person" to decide (which is completely subjective, but ignoring that), you still say that any form of eval is a built-in for the factorial, even though it evaluates code, not the factorial of a given number. Commented May 7, 2019 at 2:02

## Golfscript -- 12 chars

{,1\{)*}/}:f


### Getting started with Golfscript -- Factorial in step by step

Here's something for the people who are trying to learn golfscript. The prerequisite is a basic understanding of golfscript, and the ability to read golfscript documentation.

So we want to try out our new tool golfscript. It's always good to start with something simple, so we're beginning with factorial. Here's an initial attempt, based on a simple imperative pseudocode:

# pseudocode: f(n){c=1;while(n>1){c*=n;n--};return c}
{:n;1:c;{n 1>}{n c*:c;n 1-:n;}while c}:f


Whitespace is very rarely used in golfscript. The easiest trick to get rid of whitespace is to use different variable names. Every token can be used as a variable (see the syntax page). Useful tokens to use as variables are special characters like |, &, ? -- generally anything not used elsewhere in the code. These are always parsed as single character tokens. In contrast, variables like n will require a space to push a number to the stack after. Numbers are essentially preinitialized variables.

As always, there are going to be statements which we can change, without affecting the end result. In golfscript, everything evaluates to true except 0, [], "", and {} (see this). Here, we can change the loop exit condition to simply {n} (we loop an additional time, and terminate when n=0).

As with golfing any language, it helps to know the available functions. Luckily the list is very short for golfscript. We can change 1- to ( to save another character. At present the code looks like this: (we could be using 1 instead of | here if we wanted, which would drop the initialization.)

{:n;1:|;{n}{n|*:|;n(:n;}while|}:f

It is important to use the stack well to get the shortest solutions (practice practice practice). Generally, if values are only used in a small segment of code, it may not be necessary to store them into variables. By removing the running product variable and simply using the stack, we can save quite a lot of characters.

{:n;1{n}{n*n(:n;}while}:f

Here's something else to think about. We're removing the variable n from the stack at the end of the loop body, but then pushing it immediately after. In fact, before the loop begins we also remove it from the stack. We should instead leave it on the stack, and we can keep the loop condition blank.

{1\:n{}{n*n(:n}while}:f

Maybe we can even eliminate the variable completely. To do this, we will need to keep the variable on the stack at all times. This means that we need two copies of the variable on the stack at the end of the condition check so we don't lose it after the check. Which means that we'll have a redundant 0 on the stack after the loop ends, but that is easy to fix.

This leads us to our optimal while loop solution!

{1\{.}{.@*\(}while;}:f

Now we still want to make this shorter. The obvious target should be the word while. Looking at the documentation, there are two viable alternatives -- unfold and do. When you have a choice of different routes to take, try and weigh the benefits of both. Unfold is 'pretty much a while loop', so as an estimate we'll cut down the 5 character while by 4 into /. As for do, we cut while by 3 characters, and get to merge the two blocks, which might save another character or two.

There's actually a big drawback to using a do loop. Since the condition check is done after the body is executed once, the value of 0 will be wrong, so we may need an if statement. I'll tell you now that unfold is shorter (some solutions with do are provided at the end). Go ahead and try it, the code we already have requires minimal changes.

{1\{}{.@*\(}/;}:f

Great! Our solution is now super-short and we're done here, right? Nope. This is 17 characters, and J has 12 characters. Never admit defeat!

### Now you're thinking with... recursion

Using recursion means we must use a branching structure. Unfortunate, but as factorial can be expressed so succinctly recursively, this seems like a viable alternative to iteration.

# pseudocode: f(n){return n==0?n*f(n-1):1}
{:n{n.(f*}1if}:f # taking advantage of the tokeniser


Well that was easy -- had we tried recursion earlier we may not have even looked at using a while loop! Still, we're only at 16 characters.

### Arrays

Arrays are generally created in two ways -- using the [ and ] characters, or with the , function. If executed with an integer at the top of the stack, , returns an array of that length with arr[i]=i.

For iterating over arrays, we have three options:

1. {block}/: push, block, push, block, ...
2. {block}%: [ push, block, push, block, ... ] (this has some nuances, e.g. intermediate values are removed from the stack before each push)
3. {block}*: push, push, block, push, block, ...

The golfscript documentation has an example of using {+}* to sum the contents of an array. This suggests we can use {*}* to get the product of an array.

{,{*}*}:f


Unfortunately, it isn't quite that simple. All the elements are off by one ([0 1 2] instead of [1 2 3]). We can use {)}% to rectify this issue.

{,{)}%{*}*}:f


Well not quite. This doesn't handle zero correctly. We can calculate (n+1)!/(n+1) to rectify this, although this costs far too much.

{).,{)}%{*}*\/}:f


We can also try to handle n=0 in the same bucket as n=1. This is actual extremely short to do, try and work out the shortest you can.

Not so good is sorting, at 7 characters: [1\]$1=. Note that this sorting technique does has useful purposes, such as imposing boundaries on a number (e.g. [0\100]$1=)
Here's the winner, with only 3 characters: .!+

If we want to have the increment and multiplication in the same block, we should iterate over every element in the array. Since we aren't building an array, this means we should be using {)*}/, which brings us to the shortest golfscript implementation of factorial! At 12 characters long, this is tied with J!

{,1\{)*}/}:f

### Bonus solutions

Starting with a straightforward if solution for a do loop:

{.{1\{.@*\(.}do;}{)}if}:f


We can squeeze a couple extra out of this. A little complicated, so you'll have to convince yourself these ones work. Make sure you understand all of these.

{1\.!!{{.@*\(.}do}*+}:f
{.!{1\{.@*\(.}do}or+}:f
{.{1\{.@*\(.}do}1if+}:f


A better alternative is to calculate (n+1)!/(n+1), which eliminates the need for an if structure.

{).1\{.@*\(.}do;\/}:f

But the shortest do solution here takes a few characters to map 0 to 1, and everything else to itself -- so we don't need any branching. This sort of optimization is extremely easy to miss.

{.!+1\{.@*\(.}do;}:f

For anyone interested, a few alternative recursive solutions with the same length as above are provided here:

{.!{.)f*0}or+}:f
{.{.)f*0}1if+}:f
{.{.(f*}{)}if}:f


*note: I haven't actually tested many of the pieces of code in this post, so feel free to inform if there are errors.

• Interesting, the seems to be a bug in the spoiler markdown when you use code in a spoiler... Anyone cares to mention this on Meta? Commented Feb 7, 2011 at 11:55
• I find it interesting how golfscript - a golfing language - allows multi-letter variable names and "punishes" you for using 1 letter with necessary whitespace Commented Feb 4, 2016 at 15:45
• I see a trailing 1 when I try {:n;1:c;{n 1>}{n c*:c;n 1-:n;}while c}:f Commented Mar 23, 2020 at 19:19
• All this just to tie J... take my +1... Commented May 7, 2021 at 19:37

# Python - 27

Just simply:

f=lambda x:0**x or x*f(x-1)

• Good trick: 0**x. Commented Jul 11, 2011 at 20:25
• What about math.factorial? It isn't a built-in, is it?
– user63571
Commented Jan 19, 2017 at 20:21
• @JackBates that counts as a builtin, as you didn't write the code to compute the factorial. Commented Jan 21, 2017 at 17:51
• Can anyone tell me what's the trick behind 0**x? Commented Aug 4, 2019 at 5:36
• @Pavitra: 00=1, and it's the first thing that evaluates so it gets returned. For any other n, 0n=0, thus the first operand of or is falsey, such that the second operand gets evaluated. Commented Aug 5, 2019 at 18:13

f n=product[1..n]

• I don't know Haskell... But Will this calculate factorial for 0 Commented Feb 7, 2011 at 12:11
• @The King: yes it will. [1..0] ==> [] and product [] ==> 1
– J B
Commented Feb 7, 2011 at 12:12
• I would argue this uses the "built-in library" that the problem prohibits. Still, the other method f 0=1;f n=n*f$n-1 is 17 characters as well. Commented Jul 26, 2011 at 1:20 • @eternalmatt: that part of the restrictions is underspecified to me. Both product and, say, (*) or (-) "can calculate the factorial", and they're all defined through the Prelude. Why would one be cool and not the other? – J B Commented Jul 27, 2011 at 9:28 • @YoYoYonnY: I count 17 characters as well, for less (subjective) readability. IMHO it's fine in the comments. – J B Commented Feb 8, 2016 at 13:32 ## APL (4) ×/∘⍳  Works as an anonymous function:  ×/∘⍳ 5 120  If you want to give it a name, 6 characters: f←×/∘⍳  • I don't speak APL, what is going on here? Commented Jan 6, 2014 at 21:11 • @MichaelStern: ⍳ makes an index vector, i.e. ⍳5 is 1 2 3 4 5. × is (obviously) multiply, / is reduce, and ∘ is function composition. So, ×/∘⍳ is a function that takes an argument x and gives the product of the numbers [1..x]. Commented Jan 6, 2014 at 23:09 • Ah, the same approach as in @Yves Klett's Mathematica solution. Very nice. Commented Jan 7, 2014 at 3:14 • @NBZ: That didn't exist yet in 2011 when this question was written, nor in 2012 when I wrote this answer. Trains were only added in Dyalog 14.0 which came out in 2014. Commented Jan 25, 2016 at 18:38 • Not sure if this is what @NBZ said, but at least now, you can be shorter with ×/⍳ as this is automatically interpreted as an atop. – Tbw Commented Dec 18, 2023 at 21:07 # Mornington Crescent, 1827 1698 chars I felt like learning a new language today, and this is what I landed on... (Why do I do this to myself?) This entry won't be winning any prizes, but it beats all 0 other answers so far using the same language! Take Northern Line to Bank Take Central Line to Holborn Take Piccadilly Line to Heathrow Terminals 1, 2, 3 Take Piccadilly Line to Acton Town Take District Line to Acton Town Take District Line to Parsons Green Take District Line to Bank Take District Line to Parsons Green Take District Line to Acton Town Take District Line to Hammersmith Take Circle Line to Aldgate Take Circle Line to Aldgate Take Metropolitan Line to Chalfont & Latimer Take Metropolitan Line to Aldgate Take Circle Line to Hammersmith Take District Line to Acton Town Take Piccadilly Line to Bounds Green Take Piccadilly Line to Acton Town Take Piccadilly Line to Bounds Green Take Piccadilly Line to Acton Town Take District Line to Acton Town Take District Line to Bank Take Circle Line to Hammersmith Take District Line to Upminster Take District Line to Parsons Green Take District Line to Notting Hill Gate Take Circle Line to Notting Hill Gate Take Circle Line to Bank Take Circle Line to Temple Take Circle Line to Aldgate Take Circle Line to Aldgate Take Metropolitan Line to Chalfont & Latimer Take Metropolitan Line to Chalfont & Latimer Take Metropolitan Line to Aldgate Take Circle Line to Hammersmith Take District Line to Upminster Take District Line to Bank Take District Line to Upney Take District Line to Upminster Take District Line to Hammersmith Take District Line to Upminster Take District Line to Upney Take District Line to Bank Take Circle Line to Embankment Take Circle Line to Embankment Take Northern Line to Angel Take Northern Line to Moorgate Take Metropolitan Line to Chalfont & Latimer Take Metropolitan Line to Moorgate Take Circle Line to Moorgate Take Northern Line to Mornington Crescent  Try it online! Anyone who's journeyed around London will understand that instantly of course, so I'm sure I don't need to give a full explanation. Most of the work at the start is in handling the 0 case. After initialising the product at 1, I can use that to calculate max(input, 1) to get the new input, taking advantage of the fact that 0! = 1! Then the main loop can begin. (EDIT: A whole bunch of trips have been saved by stripping the 1 from "Heathrow Terminals 1, 2, 3" instead of generating it by dividing 7 (Sisters) by itself. I also use a cheaper method to generate the -1 in the next step.) Decrementing is expensive in Mornington Crescent (although less expensive than the Tube itself). To make things more efficient I generate a -1 by taking the NOT of a parsed 0 and store that in Hammersmith for much of the loop. I put some significant work into this, but since this is my first attempt at golfing in Mornington Crescent (in fact my first attempt in any language), I expect I missed a few optimisations here and there. If you're interested in programming in this language yourself (and why wouldn't you be?), Esoteric IDE - with its debug mode and watch window - is a must! • Why did this get so less upvotes? Commented Jul 25, 2020 at 12:10 # J, 12 bytes A standard definition in J: f=:*/@:>:@i.  Try it online! Less than 1sec for 125! Eg:  f 0 1 f 5 120 f 125x 1882677176888926099743767702491600857595403 6487149242588759823150835315633161359886688 2932889495923133646405445930057740630161919 3413805978188834575585470555243263755650071 31770880000000000000000000000000000000  • why not just */>:i. ? Commented Aug 21, 2011 at 11:26 • There's no reason it can't be an anonymous function right? Like ([:*/1+i.) for 10 points, or even 8 as the parentheses are only needed for calling the function, not for the definition. Commented Nov 4, 2014 at 22:05 • in the last one, f 125x what does the x do? Is it a special kind of number? Commented Jan 21, 2016 at 7:11 • @Cyoce, yes, it's extended precision integer. Commented Jan 21, 2016 at 19:23 • What about f=:[:*/1+i. which saves one byte? Commented Jun 24, 2016 at 8:52 ## Golfscript - 13 chars (SYM) defines the function ! {),()\{*}/}:! # happy robot version \{*}/  alternate 13 char version {),()+{*}*}:!  whole program version is 10 chars ~),()+{*}*  testcases take less than 1/10 second: input: 0!  output 1  input 125!  output 188267717688892609974376770249160085759540364871492425887598231508353156331613598866882932889495923133646405445930057740630161919341380597818883457558547055524326375565007131770880000000000000000000000000000000  • +1 for symbolic golf entry! I wish I could upvote more than once. :-D Commented Feb 7, 2011 at 0:56 • @ChrisJester-Young I'll do it for you. Commented Jan 21, 2016 at 7:30 # MATL, 2 bytes :p  Explained: : % generate list 1,2,3,...,i, where i is an implicit input p % calculate the product of of all the list entries (works on an empty list too)  Try it online! • ​​​​​​​​​:O​​​​ Commented Jan 25, 2016 at 12:14 • I was going to post exactly this :-) You may want to modify the link to include the code and an example input Commented Jan 31, 2016 at 4:56 • @AndrasDeak, No, that would output all numbers from 1 to i... – yyny Commented Feb 6, 2016 at 16:09 ## Perl 6: 13 chars $f={[*]1..$_}  [*] is same as Haskell product, and 1..$_ is a count-up from 1 to $_, the argument. • It's not allowed to not use a space after [*] anymore ("Two terms in a row" error message). – null Commented Dec 28, 2013 at 19:24 • You don't need to set a variable, a bare code block is an acceptable answer as it implicitly forms a function. Also does this still work for 0? Commented Apr 28, 2018 at 7:24 # Python 2, 28 bytes f=lambda x:x/~x+1or x*f(x-1)  Try it online! (based off Alexandru's solution) # Java (JDK), 85 bytes BigInteger f(int n){return n<2?BigInteger.ONE:new BigInteger(""+n).multiply(f(n-1));}  Try it online! • This misses the imports: import java.math.*; (so, +19 bytes). Commented Dec 24, 2017 at 10:48 • Fair point. ............ Commented Dec 29, 2017 at 19:36 # Matlab, 15 f=@(x)prod(1:x)  Test Cases >> f(0) ans = 1 >> f(4) ans = 24 >> tic,f(125),toc ans = 1.8827e+209 Elapsed time is 0.000380 seconds.  # F# (.NET Core), 26 bytes There's no inbuilt product function in F#, but you can make one with a fold let f n=Seq.fold(*)1{1..n}  Try it online! ## JavaScript, 25 function f(n)!n||n*f(n-1)  ## CoffeeScript, 19 f=(n)->!n||n*f(n-1)  Returns true in the case of n=0, but JavaScript will type-coerce that to 1 anyway. • Don't you need a return statement in the JavaScript function? Commented Jul 12, 2011 at 19:19 • Update: Holy smoke, you don't need a return! But why not? Commented Jul 12, 2011 at 19:43 • It's JavaScript 1.8 (developer.mozilla.org/en/new_in_javascript_1.8). Full disclosure, it only works on Firefox! Commented Jul 13, 2011 at 3:53 • Nice, I didn't know about leaving out the return statement for JavaScript 1.8. Also, you can guarantee 1 instead of true for the n=0 case with the same length code: function f(n)n?n*f(--n):1 Commented Aug 3, 2011 at 21:50 • ES6, 17: f=n=>!n||n*f(n-1) Take that, CoffeeScript! – Ry- Commented Dec 29, 2013 at 3:03 # Ruby, 21 bytes f=->n{n>1?n*f[n-1]:1}  Try it online! ## Test irb(main):009:0> f=->n{n>1?n*f[n-1]:1} => #<Proc:0x25a6d48@(irb):9 (lambda)> irb(main):010:0> f[125] => 18826771768889260997437677024916008575954036487149242588759823150835315633161 35988668829328894959231336464054459300577406301619193413805978188834575585470555 24326375565007131770880000000000000000000000000000000  # PostScript, 26 chars /f{1 exch -1 1{mul}for}def  Example: GS> 0 f = 1 GS> 1 f = 1 GS> 8 f = 40320  The function itself takes only 21 characters; the rest is to bind it to a variable. To save a byte, one can also bind it to a digit, like so: GS> 0{1 exch -1 1{mul}for}def GS> 8 0 load exec = 40320  • Ghostscript cannot handle 125!; anything beyond 34! comes out as 1.#INF. (I used stock GNU Ghostscript 9.0.7 compiled for x64 Windows.) Commented Jan 7, 2014 at 6:17 # Brachylog, 7 6 bytes By making a range and multiplying it -1 byte tanks to ovs having the idea to use the max() function ;1⌉⟦₁×  ## Explanation ;1 -- If n<1, use n=1 instead (zero case) ⟦₁ -- Construct the range [1,n] × -- return the product of said range  Try it online! # Brachylog, 10 9 bytes recursion ≤1|-₁↰;?×  ## Explanation  --f(n): ≤1 -- if n ≤ 1: return 1 | -- else: -₁↰ -- f(n-1) ;?× -- *n  Try it online! • This works for 6 bytes. Taking input as a singleton is allowed by default. – ovs Commented Aug 22, 2018 at 17:58 • @ovs thanks. But using ; instead of , allows for just a regular numerical input. -1byte anyway Commented Aug 22, 2018 at 18:12 # Ruby - 30 29 characters def f(n)(1..n).inject 1,:*end  Test f(0) -> 1 f(5) -> 120  • You can put the end directly after :* without a newline or semicolon. Commented Feb 6, 2011 at 17:50 • There's no need to pass 1 to the #inject call. (1..10).inject :* #=> 3628800 Commented Feb 7, 2011 at 10:56 • @Dogbert, what about for f(0)? Commented Feb 7, 2011 at 19:05 • @Nemo157, ah! forgot about that. Commented Feb 8, 2011 at 13:38 • Shorter to use 1.9 lambda syntax: f=->n{(1..n).inject 1,:*}. Call it with f[n]. Commented Aug 22, 2011 at 22:04 # Javascript, ES6 17 f=n=>n?n*f(n-1):1  ES6: • Arrow function • ES6 is younger than this challenge if I'm remembering correctly and therefore not eligible. Commented Jun 22, 2015 at 19:44 • There is smth strange with conditional operator. Why there are two colons? Commented Jun 25, 2015 at 15:43 • @Qwertiy You're right, that was a typo, thanks. Commented Jun 25, 2015 at 18:21 # C#, 20 or 39 characters depending on your point of view As a traditional instance method (39 characters; tested here): double f(int x){return 2>x?1:x*f(x-1);}  As a lambda expression (20 characters, but see disclaimer; tested here): f=x=>2>x?1:x*f(x-1);  We have to use double because 125! == 1.88 * 10209, which is much higher than ulong.MaxValue. ### Disclaimer about the lambda version's character count: If you recursion in a C# lambda, you obviously have to store the lambda in a named variable so that it can call itself. But unlike (e.g.) JavaScript, a self-referencing lambda must have been declared and initialized on a previous line. You can't call the function in the same statement in which you declare and/or initialize the variable. In other words, this doesn't work: Func<int,double> f=x=>2>x?1:x*f(x-1); //Error: Use of unassigned local variable 'f'  But this does: Func<int,double> f=null; f=x=>2>x?1:x*f(x-1);  There's no good reason for this restriction, since f can't ever be unassigned at the time it runs. The necessity of the Func<int,double> f=null; line is a quirk of C#. Whether that makes it fair to ignore it in the character count is up to the reader. # CoffeeScript, 21 19 characters for real f=(x)->+!x||x*f x-1  Tested here: http://jsfiddle.net/0xjdm971/ • Wanted to point out that while inline declaration as a Func type doesn't work, an inline function does: double f(int x)=>2>x?1:x*f(x-1); Commented Jun 8, 2020 at 17:30 # Aheui (esotope), 9390 87 bytes 박밴내색뱅뿌뮹 숙쌕빼서빼처소 타뿌싼때산쑥희 매차뽀요＠어몽  Try it online! Nice, small, and fast code. Slightly golfed after writing explanation. I'll not change it, because it is just same code. # Explaination Aheui is befunge-like language and (almost) every character of Aheui is operator. Part of character looks like ㅏ, ㅐ, ㅓ, ㅜ, ㅛ, ㅗ, ㅢ determines direction where next operator execute. ㅏ is left-to-right, ㅓ is right-to-left, ㅗ is down-to-up, ㅜ is up-to-down, ㅛ is down-to-up, with skipping one character in two characters. ㅐ is 'nothing' : keep same speed and direction. 박밴내  ㅂ commend is store given number in current stack, ㄴ commend is divide upmost two number in current stack. Both 박 and 백 store 2, so 박밴내 store 1 in current stack(default 아 or nothing stack) 색뱅  ㅅ commend change current stack. 색 change stack to 악 (or ㄱ) stack. ㅂ commend with ㅇ (like 뱅 or 방) get a number from STDIN. So 색뱅 get a number and store it in stack 악(ㄱ). 뿌 처  ㅃ commend duplicate upmost value in current stack, and ㅊ commend pop value from current stack and see if it is 0. If it is, it go to opposite direction from ㅓ indicate : in here right-to-left. If it is not, it go to direction where ㅓ indicate. So 뿌(\n)처 see if input is 0 or not, and go right if zero, and go left if not. 망희 소  If input is zero, here is evaluated. (from 소 commend) First, change current stack to nothing(아). ㅁ commend is pop, and if used with ㅇ it print value as number. 희 halts program. So it print 1 and halt. 숙쌕빼서빼 타뿌싼때산쌕꾸 매차뽀요애애어  Look at this image for help. Here is main loop. ㅌ is subtraction, and ㄸ is multiply. ㅆ move value from current stack to selected one. Put it shortly, it get number from nothing stack(or get 1), subtract to find if it is zero, and if not zero multiply and restart loop. And if zero, go to rightmost place of code with popping one number. 몽  Print number, then pointer go to 희 : halt. In one image : SEL is select, MOV is move, DUP is duplicate. This image is produced by AheuiChem, Aheui development tool in Korean. Translated with paint tool of windows. # 8088 / 8087 machine code, 13 bytes D9 E8 FLD1 ; start with 1 E3 08 JCXZ DONE ; if N = 0, return 1 FACT_LOOP: 51 PUSH CX ; push current N onto stack 8B F4 MOV SI, SP ; SI to top of stack for N DE 0C FIMUL WORD PTR[SI] ; ST = ST * N 59 POP CX ; remove N from stack E2 F8 LOOP FACT_LOOP ; decrement N, loop until N = 0 DONE: C3 RET ; return to caller  Input $$\n\$$ is in CX, output $$\{n!}\$$ is in ST(0). Test output displayed using Borland Turbo Debugger 3: n = 1: n = 15: n = 50: n = 125: Notes: • Calculates $$\{125!}\$$ in an imperceptible amount of time (difficult to accurately profile in DOS) • Language is not newer than the challenge • "Language is not newer than the challenge" facepalm Commented Mar 18, 2020 at 19:03 # C (39 chars) double f(int n){return n<2?1:n*f(n-1);}  • Nice. But can save some characters: double f(n){return!n?1:n*f(n-1);} - 33 chars. Commented Jan 12, 2012 at 16:38 • f(125) will overflow – wlad Commented Oct 14, 2015 at 7:12 • This one is 33 characters. It uses implicit int type for arguments and a more efficint ternary: double f(x){return x?x*f(x-1):1;} Commented Mar 4, 2022 at 22:29 # Jelly, 2 bytes RP  Try it online! Alternatively, a builtin answer is one byte: !  Try it online! # Pari/GP, 45 bytes x=input();forstep(y=x-1,1,-1,x=x*y);print(x);  Try it online! • Input is input. Commented Mar 5, 2022 at 1:42 • @alephalpha I know that, but how do I convert it to an integer? Commented Mar 5, 2022 at 1:43 • input reads the input as a PARI/GP expression and evaluate it. So when you input an integer, you don't need to convert. Commented Mar 5, 2022 at 1:45 • Or you can write a function instead of a full program: x->forstep(y=x-1,1,-1,x=x*y);x Commented Mar 5, 2022 at 1:45 • Or shorter: x->prod(y=1,x,y), or even x->x!. Commented Mar 5, 2022 at 1:50 # D: 45 Characters T f(T)(T n){return n < 2 ? 1 : n * f(n - 1);}  More legibly: T f(T)(T n) { return n < 2 ? 1 : n * f(n - 1); }  A cooler (though longer version) is the templatized one which does it all at compile time (64 characters): template F(int n){static if(n<2)enum F=1;else enum F=n*F!(n-1);}  More legibly: template F(int n) { static if(n < 2) enum F = 1; else enum F = n * F!(n - 1); }  Eponymous templates are pretty verbose though, so you can't really use them in code golf very well. D's already verbose enough in terms of character count to be rather poor for code golf (though it actually does really well at reducing overall program size for larger programs). It's my favorite language though, so I figure that I might as well try and see how well I can get it to do at code golf, even if the likes of GolfScript are bound to cream it. • take out the whitespace and you can get it down to 36 chars Commented Jul 3, 2011 at 13:36 • @Cyoce Can you explain? – yyny Commented Feb 6, 2016 at 16:08 • Welcome to the site, @user272735. Note that we don't edit people's solutions in order to make improvements here. Instead we leave comments suggesting those improvements, as ratchet freak did above. Commented Jul 29, 2019 at 8:29 ## PowerShell – 36 Naïve: filter f{if($_){$_*(--$_|f}else{1}}


Test:

> 0,5,125|f
1
120
1,88267717688893E+209


## Scala, 39 characters

def f(x:BigInt)=(BigInt(1)to x).product


Most of the characters are ensuring that BigInts are used so the requirement for values up to 125 is met.

• Some shorter options: (x:Int)=>(BigInt(1)to x).product def f(x:Int)=(BigInt(1)to x).product def f(x:BigInt)=(x.to(1,-1)).product def f(x:BigInt)=(-x to-1).product.abs Commented Jun 7, 2016 at 14:32

## PowerShell, 42 bytes

(saved 2 chars using filter instead of function)

filter f($x){if(!$x){1}else{$x*(f($x-1))}}


Output:

PS C:\> f 0
1
PS C:\> f 5
120
PS C:\> f 1
1
PS C:\> f 125
1.88267717688893E+209

• This is way old now, but... Can save 1 more character by reversing the if/else: filter f($x){if($x){$x*(f($x-1))}else{1}}. And it can be reduced further to 36 characters if it's called via pipeline since it's a filter (e.g. 125|f): filter f{if($_){$_*(\$_-1|f)}else{1}} Commented Oct 14, 2015 at 18:31

# Racket (scheme) 4035 29 bytes

Computes 0! to be 1, and computes 125! in 0 seconds according to timer. Regular recursive approach

(define(f n)(if(= n 0)1(* n(f(- n 1)))))


New version to beat common lisp: multiplies all elements of a list (same as that Haskell solution)

(λ(n)(apply *(build-list n add1)))


Newer version to beat the other scheme solution and math the other racket solution by using foldl instead of apply and using range instead of buildlist

(λ(n)(foldl * n(range 1 n)))
`