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Code Golf: Sierpinski's Triangle

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The challenge

The shortest code, by character count to output an ASCII representation of Sierpinski's Triangle of N iterations made from the following ASCII triangle: 

 /\
/__\

Input is a single positive number.

Test cases

Input:
    2
Output:
       /\
      /__\
     /\  /\
    /__\/__\

Input:
    3
Output:
           /\
          /__\
         /\  /\
        /__\/__\
       /\      /\
      /__\    /__\
     /\  /\  /\  /\
    /__\/__\/__\/__\

Input:
    5
Output:
                                   /\
                                  /__\
                                 /\  /\
                                /__\/__\
                               /\      /\
                              /__\    /__\
                             /\  /\  /\  /\
                            /__\/__\/__\/__\
                           /\              /\
                          /__\            /__\
                         /\  /\          /\  /\
                        /__\/__\        /__\/__\
                       /\      /\      /\      /\
                      /__\    /__\    /__\    /__\
                     /\  /\  /\  /\  /\  /\  /\  /\
                    /__\/__\/__\/__\/__\/__\/__\/__\
                   /\                              /\
                  /__\                            /__\
                 /\  /\                          /\  /\
                /__\/__\                        /__\/__\
               /\      /\                      /\      /\
              /__\    /__\                    /__\    /__\
             /\  /\  /\  /\                  /\  /\  /\  /\
            /__\/__\/__\/__\                /__\/__\/__\/__\
           /\              /\              /\              /\
          /__\            /__\            /__\            /__\
         /\  /\          /\  /\          /\  /\          /\  /\
        /__\/__\        /__\/__\        /__\/__\        /__\/__\
       /\      /\      /\      /\      /\      /\      /\      /\
      /__\    /__\    /__\    /__\    /__\    /__\    /__\    /__\
     /\  /\  /\  /\  /\  /\  /\  /\  /\  /\  /\  /\  /\  /\  /\  /\
    /__\/__\/__\/__\/__\/__\/__\/__\/__\/__\/__\/__\/__\/__\/__\/__\

Code count includes input/output (i.e full program).

language-agnostic code-golf rosetta-stone
Original Q&A
21

There are 21 answers

2
John La Rooy On BEST ANSWER

Golfscript - 46

' /\ /__\ '4/{).+: ;.{ \ ++}%\{.+}%+~ ]}@~(*n*

Golfscript - 47

' /\ /__\ '4/): ;{  +: ;.{ \ ++}%\{.+}%+}@~(*n*

Golfscript - 48

' ': '/\ /__\\'+4/{2 *: ;.{ \ ++}%\{.+}%+}@~(*n*

Golfscript - 51

~' ': '/\ /__\\'+4/\(,{;2 *: ;.{ \ ++}%\{.+}%+}%;n*

Same algorithm as my shorter python ( and ruby ) answer

Golfscript - 78

2\~(?,{-1*}$1: ;{"  ":$*. 2base.{[$$+' /\ ']=}%n+@@{[$$+"/__\\"]=}%n .2*^: ;}%

Same algorithm as my longer python solution

This one has significant newlines

2\~(?,{-1*}$1: ;{"  ":
*. 2base.{[
2*' /\ ']=}%n+@@{[
2*"/__\\"]=}%n .2*^: ;}%
1
Brian On

F#, 225 chars

let rec p n=if n=1 then" "else p(n-1)+p(n-1)
and S n=if n=1 then[" /\\ ";"/__\\"]else let s=S(n-1)in List.append(List.map(fun s->p(n)+s+p(n))s)(List.map(fun x->x+x)s)
for s in S(int(System.Console.ReadLine()))do printfn"%s"s
1
fserb On

Python, 135 chars

S=lambda n:[" /\\ ","/__\\"]if n==1 else[" "*(1<<n-1)+x+" "*(1<<n-1)for x in S(n-1)]+[x+x for x in S(n-1)]
for s in S(input()):print s
1
John La Rooy On

Python - 102

a=" /\ ","/__\\"
j=' '
for n in~-input()*j:j+=j;a=[j+x+j for x in a]+[x*2for x in a]
print"\n".join(a)

Python - 105

a=" /\ ","/__\\"
j=' '
for n in(input()-1)*j:j+=j;a=[j+x+j for x in a]+[x+x for x in a]
print"\n".join(a)

Python - 109

a=" /\ ","/__\\"
for n in range(1,input()):j=' '*2**n;a=[j+x+j for x in a]+[x+x for x in a]
print"\n".join(a)

Python2.6 - 120

N=1<<input()
a=1
while N:
 N-=2
 for s in" /\ ","/__\\":print' '*N+bin(a)[2:].replace('0',' '*4).replace('1',s)
 a=a^a*2
4
ephemient On

J

46 characters, reading from stdin.

(,.~,~[,.~' '$~#,#)^:(<:".1!:1]3)' /\',:'/__\'

\n always delimits sentences, which made it impossible to fit inside S3 (only 54 characters to play with). S4 is a bit big at 162, so I padded it to fit. Serendipitously, /\ is a legal adverb. ☺

               /\
              i=:3
             /\  /\
            %r=:1!:1
           /\      /\
          t=:]    [r+i
         /\  /\  /\  /\
        b=:' /\',:'/__\'
       /\              /\
      i=:1            -".t
     /\  /\          /\  /\
    h=:(' '$        ~#,#),.]
   /\      /\      /\      /\
  s=:(    h^:1    ,d=:    ,.~)
 /\  /\  /\  /\  /\  /\  /\  /\
(,,&(10{a.)"1[s^:(-i)b)(1!:2)(4)
2
comingstorm On

Haskell, 153 149 137 125 118 112 characters:

Using tail recursion:

(%)=zipWith(++)
p="  ":p
g t _ 1=t
g t s(n+1)=g(s%t%s++t%t)(s%s)n
main=interact$unlines.g[" /\\ ","/__\\"]p.read

earlier version, @118 characters:

(%)=zipWith(++)
f 1=[" /\\ ","/__\\"]
f(n+1)=s%t%s++t%t where t=f n;s=replicate(2^n)' ':s
main=interact$unlines.f.read

Using the (justly deprecated!) n+k pattern saved 4 characters.

I like how it comes out halfway readable even in compressed form.

edit:old main

main=do{n<-getLine;putStr$unlines$f$read n}
0
myk_raniu On

Python, 186 chars (UNIX line termination)

for j in range(1,n):
 for s in p:
  print s
 x=2**j;y=2*x;p.extend(['']*x)
 for i in range(y-1,-1,-1):
  if i<x:
   s=' '*x;p[i]=s+p[i]+s
  else:
   q=p[i-x];p[i]=q+q
0
Paul Ivanov On

Python, 120 characters (recursive solution)

S=lambda n:n<2and[" /\ ","/__\\"]or[" "*n+x+" "*n for x in S(n/2)]+[x+x for x in S(n/2)]
print"\n".join(S(1<<input()-1))

I started putting on the green where @fserb left off...

1
ephemient On

Perl

94 characters when newlines are removed.

$c=2**<>;$\=$/;for$a(0..--$c){print$"x($c-$a&~1),
map$_*2&~$a?$"x4:$a&1?'/__\\':' /\ ',0..$a/2}
0
gwell On

Lua, 139 characters

t={" /\\ ","/__\\"}for i=2,(...)do for j=1,#t do
t[#t+1]=t[j]:rep(2)k=(" "):rep(#t[j]/2)t[j]=k..t[j]..k end end
print(table.concat(t,"\n"))
7
AudioBubble On

Go, 273 characters

package main
import(f"fmt";"os";s"strconv";)func main(){var
t=[2]string{" /\\ ","/__\\"};
n,_:=s.Atoi(os.Args[1]);a:=1;N:=a<<uint(n);for
N>0{N-=2;for
k:=0;k<2;k++{for
j:=0;j<N;j++{f.Print(" ")}b:=a;for
b>0{o:=t[k];if
b&1==0{o="    "}f.Print(o);b>>=1}f.Print("\n")}a^=a*2}}

Whitespace is all significant.

Unminized with gofmt sierpinski-3.go | perl -p -e's/\t/ /g':

package main

import (
    "fmt";
    "os";
    "strconv";
)

func main() {
    var t = [2]string{" /\\ ", "/__\\"};
    n, _ := strconv.Atoi(os.Args[1]);
    a := 1;
    N := a << uint(n);
    for N > 0 {
        N -= 2;
        for k := 0; k < 2; k++ {
            for j := 0; j < N; j++ {
                fmt.Print(" ")
            }
            b := a;
            for b > 0 {
                o := t[k];
                if b&1 == 0 {
                    o = "    "
                }
                fmt.Print(o);
                b >>= 1;
            }
            fmt.Print("\n");
        }
        a ^= a * 2;
    }
}

I got a good hint for Go golf here.

10
A. Rex On

Perl, 82 strokes

This version no longer prints a trailing newline. Only the first newline is necessary:

$_=' /\ 
/__\\';
for$x(2..<>){
my$y;
$".=$";
s#.+#$y.=$/.$&x2,$".$&.$"#ge;
$_.=$y
}
print

If command-line switches are allowed, then by traditional Perl golf scoring, this is 77+3 strokes (the first newline is literal):

#!perl -p
$\=' /\ 
/__\\';
$y="",
$".=$",
$\=~s#.+#$y.=$/.$&x2,$".$&.$"#ge,
$\.=$y
for 2..$_

Please feel free to edit my answer if you find an improvement.

1
ephemient On

C

Same algorithm as the Perl answer, but weighing in heavier, at 131 necessary characters.

a,b;main(c,v)char**v;{c=1<<atoi(v[1]);for(a=0;a<c;a++,puts(""))
for(b=c;b--;write(1,b&~a?"    ":a&1?"/__\\":" /\\ ",4-2*(b>a)))--b;}

I thought write(1,…) was UNIX API, but this seems to compile and run fine on Windows too.

If you replace char by int, it saves one character and still works, but it's of questionable legality.

0
Brian Carper On

Clojure: 174 characters

Algorithm stolen from others above.

(doseq[q((fn f[n](if(= n 1)[" /\\ ""/__\\"](let[z(f(dec n))](concat(map #(let[y(repeat(Math/pow 2(dec n))\ )](apply str(concat y % y)))z)(map str z z)))))(read))](println q))

38 of those characters are parentheses. : (

(doseq [q ((fn f [n]
           (if (= n 1)
             [" /\\ " "/__\\"]
             (let [z (f (dec n))]
               (concat
                (map #(let [y (repeat (Math/pow 2 (dec n))\ )]
                        (apply str (concat y % y))) z)
                (map str z z))))) (read))] 
  (println q))
0
Jack V. On

Logo (not exactly following the requirements): 47 characters

to F:n if:n[repeat 3[F(:n-1)fd 2^:n rt 120]]end

I tested this only with http://www.calormen.com/Logo/ so I don't know if it's portable. It doesn't follow the requirements, but surely logo must be the appropriate language here? :) I love that at the time of writing logo is one character short of equalling golfscript and J.

0
gnovice On

MATLAB - 64 characters (script version)

This assumes that you have the variable N already defined in your workspace:

A=[' /\ ';'/__\'];for i=1:N-1,B=32*ones(2^i);A=[B A B;A A];end;A

MATLAB - 78 characters (m-file function version)

Pass N as an argument to the function s:

function A=s(N),A=[' /\ ';'/__\'];for i=1:N-1,B=32*ones(2^i);A=[B A B;A A];end
0
John La Rooy On

Ruby — 85

a=' /\ ','/__\\'
j=' '
2.upto(gets.to_i){j+=j;a=a.map{|x|j+x+j}+a.map{|x|x+x}}
puts a

101 chars — /\-modified solution from Rosetta Code

(a=2**gets.to_i).times{|y|puts" "*(a-y-1)+(0..y).map{|x|~y&x>0?'  ':y%2>0?x%2>0?'_\\':'/_':'/\\'}*''}
1
mob On

Sorry I'm late. This is based on A. Rex's Perl solution:

                           &I                               
                          ;for                              
                         $x  (2                             
                        ..<>){$E                            
                       .=      $E                           
                      ;my$    y;3*                          
                     33  +3  **  3;                         
                    s".+"$y.=$n.$&x2                        
                   ,$              E.                       
                  $&.$            E"ge                      
                 ;;  $_          .=  $y                     
                }print;;        sub I{($                    
               E,      $n      ,$      F,                   
              $B,$    U)=(    $",$    /,qw                  
             (/   \   _  ))  ;$  _=  $E  .$                 
            F.$B.$E.$n.$F.$U.$U.$B};33333333
0
DigitalRoss On

Nroff, 542

$ nroff -rn=5 file.n

.pl 1
.nf
.de b
. nr i 0
. while d\\$1\\ni \{\
.   \\$3 \\$1\\ni \\$2\\ni
.   nr i +1
. \}
..
.de push
. nr i 0
. while d\\$2\\ni \{\
.   nr i +1
. \}
. nr j 0
. while d\\$1\\nj \{\
.   ds \\$2\\ni \&\\*[\\$1\\nj]
.   nr i +1
.   nr j +1
. \}
..
.ds l0 \& /\[rs] \&
.ds l1 "/__\[rs]
.ds s \&\ 
.de o
. ds \\$2 \&\\*s\\*[\\$1]\\*s
..
.de p
. ds \\$2 \&\\*[\\$1]\\*[\\$1]
..
.de assign
. ds \\$2 \&\\*[\\$1]
..
.nr a 2
.while \na<=\nn \{\
. ds s \&\*s\*s
. b l m o
. b l n p
. b m l assign
. push n l
. nr a +1
.\}
.de t
\\*[\\$1]
..
.b l zz t
0
AudioBubble On

Prolog, 811 Chars

:- module(sierpinsky, [draw/1]).

% draw(+Level)
draw(N) :- K is 2^(N+1)-1,
  for(Line, 0, K),
  draw2(N, Line, true, nl),
  fail.
draw(_).

% draw2(+Level, +Line, +Before, +After)
draw2(0, 0, Before, After) :- !,
  Before, write(' /\\ '), After.
draw2(0, 1, Before, After) :- !,
  Before, write('/__\\'), After.
draw2(N, Line, Before, After) :- N>0, K is 2^N, Line < K, !, M is N-1,
  draw2(M, Line, (Before, tab(K)), (tab(K), After)).
draw2(N, Line, Before, After) :- N>0, K is 2^N, Line >= K, !, M is N-1,
  Line2 is Line - K,
  draw2(M, Line2, Before, draw2(M, Line2, true, After)).

% for(+Variable, +Integer, +Integer)
for(V, N, M) :- N =< M, V = N.
for(V, N, M) :- N < M, K is N+1, for(V, K, M).

% tab(+Integer)
tab(N) :- for(_, 1, N), write(' '), fail.
tab(_).
0
Peter Taylor On

GolfScript (45 44 chars)

~(' /\ /__\ '4/)@{.+\.{[2$.]*}%\{.+}%+\}*;n*

Similar to gnibbler's solution. My initial attempt was already quite similar, and then I looked at his and borrowed some ideas.

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