Introduction

The Dragon's Curve is a fractal curve that notably appears on section title pages of the Jurassic Park novel.

It can very simply be described as a process of folding a paper strip, as explained in the Wikipedia article about this curve.

The first few iterations of the generation of this curve look like this (credits to Wikipedia for the image):

enter image description here

The challenge

Write a program or function that, given an integer n as input, outputs the n-th iteration of the dragon curve as ASCII art using only the symbols _ and |

You have to output the figure using only |, _ and spaces. You may not output the curve as a plot or anything else.
You can take the input as a program argument, in STDIN or as a function parameter.
Inputs will always be an integer >= 0. Your program should work for reasonable values of inputs, 12 being the highest in the test cases offered.
The first iterations shall look like this
- Iteration 0 is
```
_
```
- Iteration 1 is
```
_|
```
- Iteration 2 is
```
|_ 
 _|
```
One trailing line at the end is ok. No trailing spaces allowed besides filling the line up to the rightmost character in the curve
No standard loopholes abuse as usual

Test Cases

Input 0

Output

Input 3

Output

   _   
|_| |_ 
     _|

Input 5

Output

     _   _   
    |_|_| |_ 
 _   _|    _|
|_|_|_       
  |_|_|      
    |_       
     _|      
  |_|

Input 10

Output

           _       _                                           
         _|_|    _|_|                                          
        |_|_   _|_|_   _                                       
         _|_|_| |_| |_|_|                                      
   _    |_|_|_        |_                                       
 _|_|    _| |_|        _|                                      
|_|_   _|_          |_|                                        
 _|_|_|_|_|_                                                   
|_| |_|_|_|_|_                                                 
     _|_|_| |_|                                                
    |_| |_                                                     
         _|_   _   _           _   _           _   _           
   _    |_|_|_|_|_|_|_        |_|_|_|_        |_|_|_|_         
 _|_|    _|_|_|_|_| |_|    _   _|_| |_|    _   _|_| |_|        
|_|_   _|_|_|_|_|_        |_|_|_|_        |_|_|_|_             
 _|_|_|_|_|_|_|_|_|_   _   _|_|_|_|_   _   _|_|_|_|_   _   _   
|_| |_|_|_| |_|_|_| |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_ 
     _|_|    _|_|    _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|
    |_|     |_|     |_| |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_     
                         _|_|_|_|_|_|_|_|_|_|_| |_| |_|_|_|_   
                   _    |_|_|_|_|_|_|_|_|_|_|_        |_|_|_|_ 
                 _|_|    _|_|_|_|_|_|_|_|_| |_|    _   _|_| |_|
                |_|_   _|_|_|_|_|_|_|_|_|_        |_|_|_|_     
                 _|_|_|_|_|_|_|_|_|_|_|_|_|_        |_| |_|    
                |_| |_|_|_| |_|_|_| |_|_|_|_|_                 
                     _|_|    _|_|    _|_|_| |_|                
                    |_|     |_|     |_| |_                     
                                         _|_   _   _           
                                   _    |_|_|_|_|_|_|_         
                                 _|_|    _|_|_|_|_| |_|        
                                |_|_   _|_|_|_|_|_             
                                 _|_|_|_|_|_|_|_|_|_   _   _   
                                |_| |_|_|_|_|_|_|_|_|_|_|_|_|_ 
                                     _|_|_|_|_|_|_|_|_|_|_| |_|
                                    |_| |_|_|_|_|_|_|_|_|_     
               _   _                     _|_|_| |_| |_|_|_|_   
              |_|_| |_             _    |_|_|_        |_|_|_|_ 
           _   _|    _|          _|_|    _| |_|    _   _|_| |_|
          |_|_|_                |_|_   _|_        |_|_|_|_     
            |_|_|                _|_|_|_|_|_        |_| |_|    
              |_   _       _    |_|_|_|_|_|_|_                 
           _   _|_|_|    _|_|    _|_|_|_|_| |_|                
          |_|_|_|_|_   _|_|_   _|_|_|_|_|_                     
            |_| |_| |_|_|_|_|_| |_| |_|_|_|_                   
                      |_|_|_|_        |_|_|_|_                 
                   _   _|_| |_|    _   _|_| |_|                
                  |_|_|_|_        |_|_|_|_                     
                    |_| |_|         |_| |_|

Input 12

Output

                                                               _   _           _   _                                           _   _           _   _                                           
                                                              |_|_|_|_        |_|_|_|_                                        |_|_|_|_        |_|_|_|_                                         
                                                           _   _|_| |_|    _   _|_| |_|                                    _   _|_| |_|    _   _|_| |_|                                        
                                                          |_|_|_|_        |_|_|_|_                                        |_|_|_|_        |_|_|_|_                                             
                                                            |_|_|_|_   _   _|_|_|_|_   _   _                                |_|_|_|_   _   _|_|_|_|_   _   _                                   
                                                              |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                 
                                                           _   _|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|                            _   _|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|                                
                                                          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                     
                                               _   _        |_|_|_|_|_|_|_|_|_| |_| |_|_|_|_                   _   _        |_|_|_|_|_|_|_|_|_| |_| |_|_|_|_                                   
                                              |_|_|_|_        |_|_|_|_|_|_|_|_        |_|_|_|_                |_|_|_|_        |_|_|_|_|_|_|_|_        |_|_|_|_                                 
                                           _   _|_| |_|    _   _|_|_|_|_|_| |_|    _   _|_| |_|            _   _|_| |_|    _   _|_|_|_|_|_| |_|    _   _|_| |_|                                
                                          |_|_|_|_        |_|_|_|_|_|_|_|_        |_|_|_|_                |_|_|_|_        |_|_|_|_|_|_|_|_        |_|_|_|_                                     
                                            |_|_|_|_   _   _|_|_|_|_|_|_|_|_        |_| |_|                 |_|_|_|_   _   _|_|_|_|_|_|_|_|_        |_| |_|                                    
                                              |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                                 
                                           _   _|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|                            _   _|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|                                                
                                          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_                                                     
                                            |_| |_| |_|_|_|_|_|_|_|_|_|_|_|_   _   _           _   _        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_   _   _           _   _           _   _           
                                                      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_        |_|_|_|_        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_        |_|_|_|_        |_|_|_|_         
                                                   _   _|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|    _   _|_| |_|    _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|    _   _|_| |_|    _   _|_| |_|        
                                                  |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_        |_|_|_|_        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_        |_|_|_|_        |_|_|_|_             
                                                    |_| |_| |_|_|_|_|_|_|_|_|_|_|_|_   _   _|_|_|_|_   _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_   _   _|_|_|_|_   _   _|_|_|_|_   _   _   
                                                              |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|_|_| |_|_|_|_|_|_|_|_|_|_|_| |_|_|_| |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_ 
                                                           _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|    _|_|    _|_|_|_|_|_|_|_|_|_|    _|_|    _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|
                                                          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_    |_|     |_| |_|_|_|_|_|_|_|_    |_|     |_| |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_     
                                               _   _        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|                _|_|_|_|_|_|_|_|                _|_|_|_|_|_|_|_|_|_|_| |_| |_|_|_|_   
                                              |_|_|_|_        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|_           _    |_|_|_|_|_| |_|_           _    |_|_|_|_|_|_|_|_|_|_|_        |_|_|_|_ 
                                           _   _|_| |_|    _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|    _|_|        _|_|    _|_|_|_|    _|_|        _|_|    _|_|_|_|_|_|_|_|_| |_|    _   _|_| |_|
                                          |_|_|_|_        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_    |_|         |_|_   _|_|_|_|_    |_|         |_|_   _|_|_|_|_|_|_|_|_|_        |_|_|_|_     
                                            |_|_|_|_   _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|                _|_|_|_|_|_|_|_|                _|_|_|_|_|_|_|_|_|_|_|_|_|_        |_| |_|    
                                              |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_   _            |_| |_|_|_| |_|_                |_| |_|_|_| |_|_|_| |_|_|_|_|_                 
                                           _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|                _|_|    _|_|                    _|_|    _|_|    _|_|_| |_|                
                                          |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_   _            |_|     |_|                     |_|     |_|     |_| |_                     
                                            |_| |_| |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|                                                                _|_   _   _           
                                                      |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_| |_|_                                                           _    |_|_|_|_|_|_|_         
                                                   _   _|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|    _|_|                                                        _|_|    _|_|_|_|_| |_|        
                                                  |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_    |_|                                                         |_|_   _|_|_|_|_|_             
                                                    |_| |_| |_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|                                                                _|_|_|_|_|_|_|_|_|_   _   _   
           _       _                                          |_|_|_|_|_|_| |_|_|_| |_|_|_|_|_|_   _                                                            |_| |_|_|_|_|_|_|_|_|_|_|_|_|_ 
         _|_|    _|_|                                      _   _|_|_|_|_|    _|_|    _|_|_|_|_|_|_|_|                                                                _|_|_|_|_|_|_|_|_|_|_| |_|
        |_|_   _|_|_   _                                  |_|_|_|_|_|_|_    |_|     |_| |_|_|_|_|_|_   _                                                            |_| |_|_|_|_|_|_|_|_|_     
         _|_|_| |_| |_|_|                      _   _        |_|_|_|_|_|_|                _|_|_|_|_|_|_|_|                                      _   _                     _|_|_| |_| |_|_|_|_   
   _    |_|_|_        |_                      |_|_|_|_        |_|_| |_|_           _    |_|_|_|_|_| |_|_                                      |_|_| |_             _    |_|_|_        |_|_|_|_ 
 _|_|    _| |_|        _|                  _   _|_| |_|    _   _|    _|_|        _|_|    _|_|_|_|    _|_|                                  _   _|    _|          _|_|    _| |_|    _   _|_| |_|
|_|_   _|_          |_|                   |_|_|_|_        |_|_|_    |_|         |_|_   _|_|_|_|_    |_|                                   |_|_|_                |_|_   _|_        |_|_|_|_     
 _|_|_|_|_|_                                |_|_|_|_   _   _|_|_|                _|_|_|_|_|_|_|_|                                           |_|_|                _|_|_|_|_|_        |_| |_|    
|_| |_|_|_|_|_                                |_|_|_|_|_|_|_|_|_   _            |_| |_|_|_| |_|_                                              |_   _       _    |_|_|_|_|_|_|_                 
     _|_|_| |_|                            _   _|_|_|_|_|_|_|_|_|_|_|                _|_|    _|_|                                          _   _|_|_|    _|_|    _|_|_|_|_| |_|                
    |_| |_                                |_|_|_|_|_|_|_|_|_|_|_|_|_   _            |_|     |_|                                           |_|_|_|_|_   _|_|_   _|_|_|_|_|_                     
         _|_   _   _           _   _        |_|_|_|_|_|_|_|_|_|_|_|_|_|_|                                                                   |_| |_| |_|_|_|_|_| |_| |_|_|_|_                   
   _    |_|_|_|_|_|_|_        |_|_|_|_        |_|_|_|_|_|_|_|_|_|_| |_|_                                                                              |_|_|_|_        |_|_|_|_                 
 _|_|    _|_|_|_|_| |_|    _   _|_| |_|    _   _|_|_|_|_|_|_|_|_|    _|_|                                                                          _   _|_| |_|    _   _|_| |_|                
|_|_   _|_|_|_|_|_        |_|_|_|_        |_|_|_|_|_|_|_|_|_|_|_    |_|                                                                           |_|_|_|_        |_|_|_|_                     
 _|_|_|_|_|_|_|_|_|_   _   _|_|_|_|_   _   _|_|_|_|_|_|_|_|_|_|_|                                                                                   |_| |_|         |_| |_|                    
|_| |_|_|_| |_|_|_| |_|_|_|_|_|_|_|_|_|_|_| |_|_|_| |_|_|_|_|_|_   _                                                                                                                           
     _|_|    _|_|    _|_|_|_|_|_|_|_|_|_|    _|_|    _|_|_|_|_|_|_|_|                                                                                                                          
    |_|     |_|     |_| |_|_|_|_|_|_|_|_    |_|     |_| |_|_|_|_|_|_   _                                                                                                                       
                         _|_|_|_|_|_|_|_|                _|_|_|_|_|_|_|_|                                                                                                                      
                   _    |_|_|_|_|_| |_|_           _    |_|_|_|_|_| |_|_                                                                                                                       
                 _|_|    _|_|_|_|    _|_|        _|_|    _|_|_|_|    _|_|                                                                                                                      
                |_|_   _|_|_|_|_    |_|         |_|_   _|_|_|_|_    |_|                                                                                                                        
                 _|_|_|_|_|_|_|_|                _|_|_|_|_|_|_|_|                                                                                                                              
                |_| |_|_|_| |_|_                |_| |_|_|_| |_|_                                                                                                                               
                     _|_|    _|_|                    _|_|    _|_|                                                                                                                              
                    |_|     |_|                     |_|     |_|

Scoring

This is code-golf, so the shortest program in bytes wins.

Fatalize

Posted 2015-07-12T09:35:13.633

Reputation: 32 976

I'm sure someone will complain about the vagueness of a 'huge amount of spaces', so how about an asymptotic bound? – feersum – 2015-07-12T09:52:35.940

1@feersum Well I disallowed trailing spaces altogether, so nobody will complain now! – Fatalize – 2015-07-12T09:57:52.010

2I'm complaining... now you're being a whitespace Nazi! – feersum – 2015-07-12T10:21:21.343

@feersum and you are a horizontal ellipsis Nazi! – Optimizer – 2015-07-12T12:35:48.460

This is the best fractal question ever, I hope I have time to participate! Is it ok to rotate the curve through 90,180,270 degrees or does it have to be displayed per the examples? – Level River St – 2015-07-12T13:00:33.690

@steveverrill I based the expected orientation off of the Wikipedia gif. I wouldn't mind seeing rotated curves but that would make fair scoring difficult, so sorry but it has to be outputted exactly like the examples – Fatalize – 2015-07-12T13:04:28.033

Does it need to be ASCII? I made an [SVG] answer only to find that it says it needs to be ASCII :/ – Downgoat – 2015-07-12T15:43:10.810

@vihan1086 Yes it needs to be ASCII. The whole idea for this challenge, is that this fractal is printable with only 2 ASCII characters – Fatalize – 2015-07-12T15:45:32.560

Answers

Ruby, 239 201 bytes

This is a lambda function which should be called in the same manner as the one in the ungolfed version.

Golfing improvements include: assignment of 8<<n/2 to a variable for re-use; upto loop instead of each loop; ternary operator instead of if..else..end; use of [y,y+=d].max to calculate where to print the |; use of ?_ and ?| instead of the equivalent '|'and '_'; and elimination of redundant %4 (thanks Sp3000.)

->n{a=Array.new(m=8<<n/2){" "*m}
p=q=1+x=y=m/2
r=3
1.upto(1<<n){|i|d=(r&2)-1
r%2>0?(a[y][x+=d]=?_
x+=d):(a[[y,y+=d].max][x]=?|
p=x<p ?x:p
q=x>q ?x:q)
r+=i/(i&-i)}
a.delete(a[0])
puts a.map{|e|e[p..q]}}

It relies on the following formula from Wikipedia:

First, express n in the form k*(2^m) where k is an odd number. The direction of the nth turn is determined by k mod 4 i.e. the remainder left when k is divided by 4. If k mod 4 is 1 then the nth turn is R; if k mod 4 is 3 then the nth turn is L.

Wikipedia gives the following code:

There is a simple one line non-recursive method of implementing the above k mod 4 method of finding the turn direction in code. Treating turn n as a binary number, calculate the following boolean value: bool turn = (((n & −n) << 1) & n) != 0

I improved this to i/(i&-i)%4 which uses the same technique of using the expression i&-i to find the least significant digit but my expression gives 1 (for left turn)or 3 (for right turn) directly, which is handy as I track direction as a number 0..3 (in order north, west, south, east for golfing reasons.)

Ungolfed original in test program

f=->n{
  a=Array.new(8<<n/2){" "*(8<<n/2)}  #Make an array of strings of spaces of appropriate size 
  p=q=1+x=y=4<<n/2                   #set x&y to the middle of the array, p&q to the place where the underscore for n=0 will be printed.                             
  r=3                                #direction pointer, headed East
  (1..1<<n).each{|i|                 #all elements, starting at 1
    d=(r&2)-1                          #d is +1 for East and South, -1 for West and North
    if r%2>0                           #if horizontal
      a[y][x+=d]='_'                     #move cursor 1 position in direction d, print underscore,
      x+=d                               #and move again.
    else                               #else vertical
      a[(y+([d,0].max))][x]='|'          #draw | on the same line if d negative, line below if d positive
      y+=d                               #move cursor
      p=x<p ?x:p                         #update minimum and maximum x values for whitespace truncation later
      q=x>q ?x:q                         #(must be done for vertical bars, to avoid unnecesary space in n=0 case)
    end
    r=(r+i/(i&-i))%4                   #update direction
  }
  a.delete(a[0])                     #first line of a is blank. delete all blank lines.
  puts a.map!{|e|e[p..q]}                 #use p and q to truncate all strings to avoid unnecessary whitespace to left and right.
}


f.call(0)
f.call(2)
f.call(3)
f.call(11)

Level River St

Posted 2015-07-12T09:35:13.633

Reputation: 22 049

@Fatalize both functions are (currently) identical (except for the comments and whitespace.) I've added printing to stdout instead of returning a value (+5 bytes) and deleted the f= at the beginning as this is not normally counted for an anonymous function definition (-2 bytes.) More golfing tomorrow. Note that you will still have to execute the golfed function, by assigning it to a variable f=->n{.....} and calling it using f.call(n) as in the test program example. – Level River St – 2015-07-13T21:30:25.270

1@Fatalize BTW I think the fractal looks absolutely awesome in my console. Thanks for the challenge. – Level River St – 2015-07-13T21:32:21.823

@Sp3000 indeed %4 is not necessary, as r is only used in the expressions r%2 and r&2. Thanks for the tip. I'm now down to 202. – Level River St – 2015-07-14T22:16:39.583

Python 2, 270 222 bytes

y=X=Y=0
i=m=x=1
D={}
k=2**input()
while~k+i:j=Y+(y>0);s={2*X+x};D[j]=D.get(j,s)|s;m=min(m,*s);Y+=y;X+=x;exec i/(i&-i)*"x,y=y,-x;";i+=1
for r in sorted(D):print"".join(" | _"[(n in D[r])+n%2*2]for n in range(m,max(D[r])+1))

Now using the formula for the nth turn. I saw the (((n & −n) << 1) & n) formula on Wikipedia, but didn't realise how useful it was until I saw it in @steveverrill's answer. I actually drop the %4 as well, so there's a lot of rotating going on, making larger inputs take a while.

Side remark: This isn't graphical output, but here's some golfed turtle code:

from turtle import*
for i in range(1,2**input()+1):fd(5);lt(i/(i&-i)*90)

Sp3000

Posted 2015-07-12T09:35:13.633

Reputation: 58 729

As long as it doesn't take an hour to run, it's fine by me – Fatalize – 2015-07-12T15:14:09.723

If I understand correctly, your second code could be changed very slightly to become an answer to this challenge.

– nedla2004 – 2016-11-22T02:08:08.557

C#, 337 bytes

There's a bit of rules abuse here. There's no restriction on leading space. Unfortunately, the canvas is finite, so there is an upper limit for n.

Indented for clarity:

using C=System.Console;
class P{
    static void Main(string[]a){
        int n=int.Parse(a[0]),d=2,x=250,y=500;
        var f="0D";
        while(n-->0)
            f=f.Replace("D","d3t03").Replace("T","10d1t").ToUpper();
        C.SetBufferSize(999,999);
        foreach(var c in f){
            n=c&7;
            d=(d+n)%4;
            if(n<1){
                var b=d%2<1;
                x+=n=b?1-d:0;
                y+=b?0:2-d;
                C.SetCursorPosition(x*2-n,y+d/3);
                C.Write(b?'_':'|');
            }
        }
    }
}

Hand-E-Food

Posted 2015-07-12T09:35:13.633

Reputation: 7 912

JavaScript (ES6), 220

Using the wikipedia formula for left and right turns.

n=>(d=>{for(i=x=y=d;i<1<<n;d+=++i/(i&-i))z=d&2,(w=d&1)?y+=z/2:x+=1-z,g=x<0?g.map(r=>[,,...r],x=1):g,g=y<0?[y=0,...g]:g,r=g[y]=g[y]||[],r[x]='_|'[w],w?y-=!z:x+=1-z})(0,g=[])||g.map(r=>[...r].map(c=>c||' ').join``).join`
`

Less golfed

n=>{
  g=[];
  for(i=x=y=d=0;i<1<<n;d+=++i/(i&-i))
    z=d&2,
    (w=d&1)?y+=z/2:x+=1-z,
    g=x<0?g.map(r=>[,,...r],x=1):g,
    g=y<0?[y=0,...g]:g,
    r=g[y]=g[y]||[],
    r[x]='_|'[w],
    w?y-=!z:x+=1-z
  return g.map(r=>[...r].map(c=>c||' ').join``).join`\n`
}

F=
n=>(d=>{for(i=x=y=d;i<1<<n;d+=++i/(i&-i))z=d&2,(w=d&1)?y+=z/2:x+=1-z,g=x<0?g.map(r=>[,,...r],x=1):g,g=y<0?[y=0,...g]:g,r=g[y]=g[y]||[],r[x]='_|'[w],w?y-=!z:x+=1-z})(0,g=[])||g.map(r=>[...r].map(c=>c||' ').join``).join`
`

function update() {
  var n=+I.value
  O.textContent=F(n)
}

update()

pre { font-size: 8px }

<input id=I value=5 type=number oninput='update()'><pre id=O></pre>

edc65

Posted 2015-07-12T09:35:13.633

Reputation: 31 086

APL (Dyalog Unicode), 65 64 bytes^SBCS

('_|'⍴⍨≢a)@a⍴∘''⊃1+⌈/a←(⊢-⌊/)⌈2+/÷∘¯2 1¨11 9∘○¨+\0,(⊢,0j1×⌽)⍣⎕,1

Try it online!

(⊢,0j1×⌽)⍣⎕,1 generates a list of steps as complex numbers. It starts from 1 and repeatedly appends (,) a reversed (⌽) copy of the list multiplied by 0j1=sqrt(-1).

+\0, prepend 0 and compute prefix sums

11 9∘○¨ decompose complex into (real;imaginary) pairs

÷∘¯2 1¨ divide the real parts by -2

2+/ sums of adjacent pairs

⌈ ceiling

(⊢-⌊/) subtract the minima from all, so that coords are non-negative

a← assign to a

⍴∘''⊃1+⌈/ create an empty char matrix such that the max coords can fit

('_|'⍴⍨≢a)@a put alternating _ and | at the coordinates from a

ngn

Posted 2015-07-12T09:35:13.633

Reputation: 11 449

ASCII Dragon's Curve

Introduction

The challenge

Test Cases

Scoring

Answers

Ruby, 239 201 bytes

Python 2, 270 222 bytes

C#, 337 bytes

JavaScript (ES6), 220

APL (Dyalog Unicode), 65 64 bytesSBCS

APL (Dyalog Unicode), 65 64 bytes^SBCS