The IHIH Pyramid

I find it fascinating how the letters "H" and "I" are very similar. "H" is a horizontal stroke surrounded by two vertical strokes; "I" is a vertical stroke surrounded by two horizontal strokes (depending on your font). I bet this could be nested... You know what that reminds me of? Fractals!!!

Let's define the "IHIH" pyramid as follows: The first iteration is this ASCII representation of the letter "I":

---
|
---


The next iteration has a vertical stroke on either side.

|   |
|---|
| | |
|---|
|   |


If you view the "I" in the middle as a single horizontal stroke, then this second iteration is basically an "H". The third iteration adds a horizontal stroke on the top and bottom

-------
|   |
|---|
| | |
|---|
|   |
-------


Again, if you view the "H" in the middle as a single vertical stroke, then this iteration is basically an "I". This pattern continues, alternating between "H"s and "I"s on every iteration. For reference, here are the first 6 iterations:

1:
---
|
---

2:
|   |
|---|
| | |
|---|
|   |

3:
-------
|   |
|---|
| | |
|---|
|   |
-------

4:
|       |
|-------|
| |   | |
| |---| |
| | | | |
| |---| |
| |   | |
|-------|
|       |

5:
-----------
|       |
|-------|
| |   | |
| |---| |
| | | | |
| |---| |
| |   | |
|-------|
|       |
-----------

6:
|           |
|-----------|
| |       | |
| |-------| |
| | |   | | |
| | |---| | |
| | | | | | |
| | |---| | |
| | |   | | |
| |-------| |
| |       | |
|-----------|
|           |


The Challenge:

Write a program or function that outputs the N'th iteration of the IHIH pyramid, and an optional trailing newline. Your input will be a single positive integer in whatever reasonable format you want. You do not have to handle invalid inputs, e.g. non-integers, numbers smaller than 1, etc. Your program must at the very least produce the right output for inputs up to 20. Since this is , standard loopholes are not allowed and the shortest answer in bytes wins!

• Is it acceptable if I return an arrow of strings one fror each row? – Rohan Jhunjhunwala Aug 19 '16 at 1:13
• Didn't quite meeting the challenge criteria, but did something cool by accident... Try it online! – Magic Octopus Urn May 21 '18 at 14:09

Pyth, 504031 25 bytes

j@s.u,J+*\-K+2lheN+jR*2;eN*\-KjR"||"+*dK+J*dKQ]]\|
LXR"|-")CbjyW%Q2uy+K*\-+2lhG+jR*2;GKQ]\|
juCGQuC+K*@"-|"H+3yH+jR*2;GKQ\|
j@CBujR*@"-|"H2CjR*2;GQ\|


Test suite.

Explanation

This is a recursive algorithm.

In each iteration, we perform three actions:

1. prepend and append a space to each line
2. transpose the array
3. prepend and append to each line either "-" or "|" depending on the number of iteration.

After the iterations, the odd-numbered outputs will be transposed. Therefore, we transpose them.

j@CBujR*@"-|"H2CjR*2;GQ\|   input: Q
j@CBujR*@"-|"H2CjR*2;GQ\|Q  implicit filling of arguments

u                 Q\|   for Q times, starting with "|", G as current output,
H as number of iterations:

jR*2;G          prepend and append a space to each line
(using each line as separator, join [" "," "])
C                transpose
jR*      2                 prepend and append the following to each line:
@"-|"H                      the H-th element of the string "-|" (modular indexing)

@CB                     Q  select the Q-th element from [output,
transposed output] (modular indexing)
j                           join by newlines

• I love the transponation idea. – Titus Aug 26 '16 at 3:46

Python, 165145133 123 bytes

A recursive solution:

def i(e):
d="|";a=e*2;x=d+" "*(a-1)+d
if e<1:return d
if e%2:d,x=[" ","-"*(a+1)]
return[x]+[d+z+d for z in i(e-1)]+[x]


Called with print ("\n".join(i(int(sys.argv[1])))), where the parameter is the iteration number of the IHIH pyramid.

Thanks to @DJMcMayhem for saving 20 bytes. Taking the idea behind those suggestions further saved another 12 bytes. Thanks to @Maltysen for suggestions that trimmed some more bytes.

The function sets the delimiter d to "|" and the intervening spaces to " " (for odd-numbered iterations), deals with returning in the degenerate case, then resets the delimiter to " " and the intervening spaces to "-" for even-numbered iterations. The function returns a list of strings for each line of the IHIH, having embedded the result of a recursive call to the function in the right place within the list.

• Nice answer, and welcome to the site! You do not need to join the lines, a list of strings is fine. A couple tips: change lines 2 and 3 to if e<1:return'|' (no newline between them) then remove the "else" and remove the extra indentation. – James Aug 19 '16 at 2:28
• you can take out the space after return. Also, you can merge the lines without ifs with semicolons, and save on the indentation – Maltysen Aug 19 '16 at 3:11
• I've edited your answer. Please feel free to revert my edits if you don't like them. – Leaky Nun Aug 19 '16 at 3:43

Cheddar, 186177165154148 131 bytes

(n,b?,c?,q?,g=s->(n-=1)<0?s:g((q=(c=s.lines[0].len)%4>2?b='|'+" "*c+"|":b='-'*(c+2))+"\n"+s.sub(/^|$/gm,q?'|':' ')+"\n"+b))->g("|")  Uses recursion. Will add explanation once done golfing. Try it online! Explanation This one is a bit complex too keep track off all the variables I'm using but I'll try to keep it simple: ( n, // Input b?, // Stores row to add to top/bottom c?, // Width of string q?, // false if I-ifying. true if not g= s-> // Main logic, s is generated string (n-=1)<0 ? s : // Decrease input each iteration. Stop when 0 g( // Recurse with.... ( q= ( // Set q true if h-ifying. false if I-ifying c=s.lines[0].len // Set c to width of string ) % 4>2 ? b='|'+" "*c+"|" : // Set b to top/bottom row adding b='-'*(c+2) // * is repeat, c is from before ) + "\n" + s.sub(/^|$/gm,       // Add the following to beginning/end of each line
q?'|':' '          // if H-ifying, add |s if I-ifying add spaces
) + "\n" + b         // Add bottom row, generated from before
)
) -> g("|")     // Middle item is |


This was a pain to golf but its 55 bytes shorter than original.

Python 2, 93 bytes

Leaky Nun saved 7 bytes.

r=range(input()+1)
r=r[:0:-1]+r
for y in r:print''.join('| -'[[x%2,y%2+1][x&-2<y]]for x in r)

• Closed form :o :o – Leaky Nun Aug 19 '16 at 12:52
• Ahh, of course: at first I needed int(x/2.) because I was taking range(-n,n+1) but now I can just use those. Thank you! – Lynn Aug 19 '16 at 13:03
• I specified Python 2 in the header because simply saying "Python" usually means the code works under either Python 2 or Python 3, which is not the case here. – Mego Aug 19 '16 at 13:33

Matricks, 80 62 bytes

An iterative solution (Recursion in Matricks is hard...)

Run with python matricks.py ihih.txt [[]] <input> --asciiprint

k124;FiQ%2:v;b[m124:Q*2+3:1;];a{z:Q*2+1;};:b;v[m45:1:Q*2+3;];u{zQ*2+1:;};;:1:n;;
k124;FiQ%2:v;b[m124:Q*2+3:2;];B1;:b;v[m45:2:Q*2+3;];V1;;:1:n;;


Explanation:

k124;                 # Set the matrix to '|'
F...:1:n;;            # Repeat input times, (Q is iteration variable)
iQ%2:...:...;       # if statement, check if Q is odd or even
# Q is even,
b;                # Make space to the left
v[m45:2:Q*2+3;];  # Set the top 2 rows to '-'s
V1;               # Rotate the matrix up 1 unit, moving the topmost row to the bottom
# Q is odd,
v;                # Make space above
b[m124:Q*2+3:2;]; # Set the 2 left columns to '|'s
B1;               # Rotate the matrix left 1 unit, moving the leftmost row to the right

• Wow, iterative! I'm impressed. – Conor O'Brien Aug 19 '16 at 3:41
• @ConorO'Brien Matricks was built for dynamic matrix resizing, so it's not THAT impressive, but thanks anyway! – Blue Aug 19 '16 at 3:42

JavaScript (ES6), 92 90 bytes

f=
(n,[h,c,v]=n&1?-- : ||)=>n?(c+=h.repeat(n+n-1)+c)+
${f(n-1).replace(/^|$/gm,v)}
+c:v
;
<input type=number min=0 oninput=o.textContent=f(+this.value)><pre id=o>

Recursive solution works by taking the previous iteration, adding the v character to the sides, then adding the c character to the corners and the h character along the top and bottom. The set of characters simply alternates each iteration. Edit: Saved 2 bytes by returning v when n=0.

Dyalog APL, 52 43 bytes

{v=⊃⍵:h⍪⍨h⍪s,⍵,s⋄v,⍨v,s⍪⍵⍪s}⍣⎕⍪⊃v h s←'|- '


v h s←'|- ' assigns the three characters to three names (vertical, horizontal, space)

⊃ the first one, i.e. |

⍪ make into 1×1 table

{...}⍣⎕ get input and apply the braced function that many times

v=⊃⍵: if the top-left character of the argument is a vertical, then:

h⍪⍨ horizontals below

h⍪ horizontals above

s, spaces to the left of

⍵,s the argument with spaces to the right

⋄ else:

v,⍨ verticals to the right of

v, verticals to the left of

s⍪ spaces above

⍵⍪s the argument with spaces below

TryAPL online!

Brachylog, 84 bytes

,[[["|"]]:?:1]i:1:zi:ca~@nw
hh~m["-|":B]:ramggL," "ggS,?:Sz:ca:Srz:caz:Lz:ca:Lrz:ca.


Try it online!

A port of my answer in Pyth.

C, 110 bytes

#define R(A,B,C)for(A=n,B=1;A<=n;putchar(C),A-=B|=-!A)
f(n,y,x,w,v){R(y,w,10)R(x,v,"| -"[x/2*2<y?y%2+1:x%2]);}


Invoke as f(n). For 111 bytes, I could do:

f(n,y,x,w,v){for(y=n,w=1;y<=n;y-=w|=-!y,puts(""))for(x=n,v=1;x<=n;x-=v|=-!x)putchar("| -"[x/2*2<y?y%2+1:x%2]);}


i.e., the #define saves exactly one byte.

Dyalog APL, 34 bytes

{⍉⍣⍵{b,b,⍨⍉s,⍵,⊃s b←' -|'~⊃⍵}⍣⍵⍪'|'}


{...}⍣⍵⍪'|' Apply function in braces ⍵ times starting with 1x1 matrix of character |. The result of each application is the argument for the next application.

s b←' -|'~⊃⍵ s is space and b is the bar not in the top left corner of the argument (' -|'~'-' removes horizontal bar and leaves space and vertical bar)

s,⍵,⊃s b add space to left and right (⊃ picks s from vector s b)

b,b,⍨⍉ transpose and add b to left and right

For odd numbers this leaves the result transposed, so a final transpose is required.

⍉⍣⍵ Transpose ⍵ times (once would be enough, but shorter to code this way)

TryAPL online

• Welcome to PPCG! – Stephen Aug 18 '17 at 21:24
• Thanks! Trying to join the party now, lots of fun solving these :) – Gil Aug 18 '17 at 21:31

Cheddar, 107 bytes

(n,g=n->n?(f->f(f(g(n-1)," ").turn(1),n%2?"-":"|"))((a,b)->a.map(i->b+i+b)):["|"])->(n%2?g(n).turn(1):g(n))


Try it online!

Cheddar, 85 bytes

(n,r=(-n|>n).map(v->abs v))->r.map(y->r.map(x->"| -"[(x&-2)<y?y%2+1:x%2]).fuse).vfuse


My first Cheddar answer. Try it online!

If I try to write r=(-n|>n).map(v->abs v).map, and then r(y->r(x->…)), the interpreter crashes. ;-;

• You can make v->abs v into (abs) (e.g. r.map((abs))) which will return a function which has the behavior of the abs function. e.g. (+)(1,2) -> 3. (^)(2,6) -> 64. Also big wow on outgolfing me by almost 50% – Downgoat Aug 20 '16 at 19:09
• No, I tried that: Runtime Error: abs has no behavior for types Number and Number  (because map receives both the element and its index, presumably.) – Lynn Aug 20 '16 at 20:34
• ah :/ i was just about to fix that bug today >_> – Downgoat Aug 21 '16 at 1:12

APL (Dyalog Classic), 34 bytes

'- |'[2+∘.(≤-(1+=)×2|⌈)⍨(⌽,0,⊢)⍳⎕]


Try it online!

(uses ⎕io←1)

⍳⎕ is 1 2 ... N

(⌽,0,⊢) is a train that turns it into -N ... -1 0 1 ... N

∘.( )⍨ executes the parentheses for every pair of coordinates ⍺ ⍵

the train (≤-(1+=)×2|⌈) or its dfn equivalent {(⍺≤⍵)-(1+⍺=⍵)×2|⍺⌈⍵} produces a matrix like:

 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1
0  1  0  0  0  0  0  0  0  1  0
0  1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1  1  0
0  1  0  1  0  0  0  1  0  1  0
0  1  0  1 ¯1 ¯1 ¯1  1  0  1  0
0  1  0  1  0  1  0  1  0  1  0
0  1  0  1 ¯1 ¯1 ¯1  1  0  1  0
0  1  0  1  0  0  0  1  0  1  0
0  1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1  1  0
0  1  0  0  0  0  0  0  0  1  0
¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1


'- |'[2+ ] makes these valid indices in ⎕IO=1 and picks the corresponding characters

Ruby, 8178 77 bytes

This is based on Lynn's Python answer. Golfing suggestions welcome.

Edit: 3 bytes thanks to Lynn. Corrections and golfing 1 byte thanks to Jordan.

->n{r=(-n..n).map &:abs;r.map{|y|puts r.map{|x|"| -"[x&-2<y ?y%2+1:x%2]}*""}}


Ungolfing:

def f(n)
r = -n..n            # Range from -n to n (inclusive)
r = r.map{|i|i.abs}  # Turns every element of r positive
r.each do |y|
s = ""             # a line of the fractal
r.each do |x|      # build up the fractal based on x and y
if x/2*2 < y
s += " -"[y%2]
else
s += "| "[x%2]
end
end
puts s             # print the line
end
end

• Can you .map(&:abs)? – Lynn Aug 19 '16 at 13:31
• @Lynn Well spotted. Any other suggestions? – Sherlock9 Aug 19 '16 at 13:37
• The first * isn't doing anything. You can use *"" instead of .join. Also, using p surrounds each line with quotation marks (it calls inspect on its arguments), which might disqualify you. – Jordan Aug 20 '16 at 0:26
• Also, you can remove the parentheses around &:abs (map &:abs). You might be able to do something with Array#product instead of nested maps, but it'll make line breaks tricky. – Jordan Aug 20 '16 at 0:42
• @Jordan Your first four hints work, but r.product(r).map (however that works) is longer and does not appear to allow line breaks very easily. – Sherlock9 Aug 20 '16 at 7:42

MATLAB, 168 163 bytes

This is probably not the cleverest way to do it: Expanding a string on all sides in n steps:

function s=g(n);s='|';for m=1:n;if mod(m,2);a=45;b=a;c=0;else a='|';b=0;c=a;end;s=[a repmat(b,1,2*m-1);repmat(c,2*m-1,1) s];s(:,end+1)=s(:,1);s(end+1,:)=s(1,:);end


Usage: Save as g.m (do I have to add that to the byte count?) and call e.g. g(15).

Ungolfed:

function s=g(n)

% // Initialize s
s = '|';

for m=1:n
% // Decide if odd or even number and which symbol to add where
if mod(m,2)
a=45;b=a;c=0; % // char(45) is '-' and char(0) is ' ' (thx to Luis Mendo)
else
a='|';b=0;c=a;
end
% // Add symbols at top and left to s
s = [a repmat(b,1,2*m-1);repmat(c,2*m-1,1) s];
% // Add symbols at right and bottom to s
s(:,end+1) = s(:,1);
s(end+1,:) = s(1,:);
end

• You can replace ' ' by 0 (Matlab treats char 0 as a space) and '-' by 45. File name doesn't have to be included in byte count – Luis Mendo Aug 19 '16 at 9:41

Actually, 4845 44 bytes

This is an attempt to port my Ruby answer to Actually. This is way too long and golfing suggestions are very much appreciated. Try it online!

u;±ux♂A╗╜╝╜";2@%2╛%u╛(2±&<I'-' '|++E"£MΣ.M


Here is a 46-byte version which separates out the nested functions so that we can define "| -" in fewer bytes. Try it online!

u;±ux♂A╗╜;2@%2╛%u╛(2±&<I"| -"E#"╝╜%r£MΣ."%£M


Ungolfing:

First algorithm

u         Increment implicit input.
;±u       Duplicate, negate, increment. Stack: [-n n+1]
x♂A       Range [-n, n+1). Abs(x) over the range.
╗         Save list to register 0. Let's call it res.
╜         Push res so we can iterate over it.
         Start function (with y from map() at the end)
╝         Save y to register 1.
╜         Push res so we can iterate over it.
"         Start function as string (with x from map() at the end)
;         Duplicate x.
2@%       x mod 2.
2╛%u      y mod 2 + 1.
╛(2±&<I   If x&-2 < y, then y%2+1, else x%2.
'-' '|++  Push "| -" (We're inside a string right now,
so we need to push each char individually)
E         Grab index of "| -"
"£        End string and turn into function.
M         Map over res.
Σ.        sum() (into a string) and print.
End function.
M         Map over res.


Second algorithm

u;±ux♂A╗╜                  Create res as before.
;2@%2╛%u╛(2±&<I"| -"E#   The inner function from the first algorithm put into a list.
The only change to the function is the definition of "| -".
"╝╜  £MΣ."                 Most of the outer function from the first algorithm as a string.
%r      %               %-formats the list into the outer function.
£M             Turns the string into a function, maps over res.

• u;±ux♂A╗╜;2@%2╛%u╛(2±&<I"| -"E#"╝╜%r£Mεj."%£M is longer than what you currently have (by 2 bytes), but you might find some inspiration for ways to make it shorter that I'm not seeing. – Mego Aug 21 '16 at 7:48

Canvas, 191817 14 bytes

|╶［ ｅ↷ｌ|＊ｅ｝╶［↷


Try it here!

If I were allowed to output every other output rotated 90°, the last 4 characters could be removed.

Explanation (some characters have been changed to look ~monospace):

|               push "|" - the canvas
╶[       }     repeat input times
e             encase the canvas in spaces horizontally
↷            rotate the canvas 90°
l|*         push "-" repeated the canvas height times vertically
e        and encase the canvas if two of those horizontally
╶[   repeat input times
↷    rotate the canvas 90°

• I'd lose 6 bytes if they loosened that restriction too :P. – Magic Octopus Urn May 21 '18 at 15:45
• @MagicOctopusUrn wellp, make that -5 bytes for me :p (could your answer benefit from a transpose loop as well?) – dzaima May 21 '18 at 16:15
• my implementation is a transpose loop :D. – Magic Octopus Urn May 21 '18 at 16:48

05AB1E, 29 28 bytes

„|-S¹>∍ƶćsvy‚˜.Bζ}¹Fζ}»R.∞.∊


Try it online!

-1 thanks to Dzaima...

This is an iterative solution.

Essentially This is made by creating the following pattern:

['|','--','|||',...]


By transposing after each iteration, we end up creating a single corner of the pattern.

Then, we can use 05AB1E's reflection commands.

„|-S                         # Push ['|','-']
¹>∍                      # Extended to input length.
ƶ                     # Each element multiplied by its index.
ćs                   # Extract head of list, swap remainder to top.
v      }           # For each element in the '|-' list...
y‚˜               # Wrap current 2D array with new entry, flatten.
.Bζ            # Pad and transpose, leaving it transposed for the next addition.
}           # End loop.
¹Fζ}       # Transpose N times.
»R     # Bring it all together into a newline string, reverse.
.∞.∊ # Mirror horizontally, then vertically with overlap.


Mathematica, 158 164 bytes

f[n_]:=Print/@StringJoin/@Map[{{{"|","|", },{ , , }},{{"|", ,"-"},{ ,"-","-"}}}[[##]]&@@#&,Table[{1+i~Mod~2, 1+j~Mod~2, 2+Sign[Abs[i]-Abs[j]]}, {i,-n,n}, {j,-n,n}],{2}]


Mathematically calculates the correct symbol at the coordinates (i,j), where both run from -n to n. Human formatted:

f[n_]:=Print/@
StringJoin/@
Map[
{{{"|","|", },{ , , }},{{"|", ,"-"},{ ,"-","-"}}[[##]]&@@#&,
Table[{1+i~Mod~2,1+j~Mod~2,2+Sign[Abs[i]-Abs[j]]},{i,-n,n},{j,-n,n}],
{2}]

• @Adám Thank you for the pointer to that thread! – Greg Martin Aug 19 '16 at 16:40

PHP, 166 bytes

golfed more than 100 bytes off my first approach and it´s still the longest answer here.

function i($n){for($m=['|'];$k++<$n;){array_unshift($m,$m[]=str_repeat(' -'[$f=$k&1],2*$k-1));foreach($m as$i=>&$r)$r=($c='||- '[2*$f+($i&&$i<2*$k)]).$r.$c;}return$m;}  breakdown function h($n)
{
for($m=['|'];$k++<$n;) { array_unshift($m,$m[]=str_repeat(' -'[$f=$k&1],2*$k-1));
foreach($m as$i=>&$r)$r=($c='||- '[2*$f+($i&&$i<2*$k)]).$r.$c; } return$m;
}


ungolfed

function ihih($n) {$m=['|'];                   // iteration 0
for($k=1;$k<=$n;$k++)       // loop $k from 1 to$n
{
$f=$k&1;                        // flag for odd iterations
$r=str_repeat(' -'[$f],2*$k-1); // new line: ' ' for even, '-' for odd iterations$m[]=$r; // append array_unshift($m,$r); // prepend // add columns: foreach($m as$i=>&$r)           // for each line
{
$c='| '[$f];                        // '|' for even, ' ' for odd iterations
if($f && (!$i || $i==2*$k)) $c='-'; // '-' in corners for odd iterations$r=$c.$r.$c; // prepend and append character } } return$m;
}


Perl 5, 150 bytes

sub h{my$i=pop;my$c=$i%2?$":'|';return(map{"$c$_$c"}h($i-1)),$i%2?'-'x($i*2+1):$c.$"x($i*2-1).$c if$i;()}say for reverse(@q=h<>),$q[0]=~s/---/ | /r,@q


Try it online!

f 0=["|"]
f n|odd n=g ' '!n$'-'|1>0=g '|'$id!n$' ' g c=map$(c:).(++[c])
(g!n)c|p<-g.f$n-1=(:p)<>pure$c<$head p  Try it online! Explanation/Ungolfed The helper function g takes a character and a list of strings, it then pre- and appends that character to each string: g c = map (\s-> [c] ++ s ++ [c])  Next the operator (!) takes a function (g), a number (n) and a character (c). It then computes the output for n-1, applies the function g to it and adds a string of the same width consisting of cs to the beginning and end: (g ! n) c | prev <- g$ f (n-1), ln <- [c | _ <- head p]
= [ln] ++ prev ++ [ln]


With these we'r ready to generate the outputs recursively, first we need to cover the base case:

f 0 = ["|"]


And then the recursion:

-- for odd n: the previous output needs a space at the end and beginning and then a string of '-' characters at the top and bottom
f n | odd n     = (g ' ' ! n) '-'
-- for even n: the previous output needs a line of spaces at the top and bottom and then each line needs to be enclosed with '|' characters
| otherwise = g '|' \$ (id ! n ) ' '


J, 37 bytes

f=:{&' |-'@*@(-:@=+<-2&|@>.)"{~@:|@i:


TIO

Stax, 22 bytes

âeò↕\┐▄┤╚╬8φ8Δ☺Pä≤δ₧ßƒ


Run and debug it

Unpacked, ungolfed, and commented, it looks like this.

'|          string literal "|"
{           begin block to repeat
. |G      push " |", then jump to trailing } below
'-z2lG    push ["-",[]], then jump to trailing } below again
}N          repeat block according to number specified in input
m           output each row in grid

}           goto target - G from above jumps to here
i@        modularly index into pair using iteration index
~         push to input stack
{;|Sm     surround each row with the extracted element
M         transpose grid


Run this one