Fold a string into a triangle

Question

Given a string whose length is divisible by 4, make a triangle as demonstrate below.

If the string is abcdefghijkl, then the triangle would be:

 a
 b l
 c k
defghij

If the string is iamastringwithalengthdivisiblebyfour, then the triangle would be:

 i
 a r
 m u
 a o
 s f
 t y
 r b
 i e
 n l
gwithalengthdivisib

If the string is thisrepresentationisnotatriangle, then the triangle would be:

 t
 h e
 i l
 s g
 r n
 e a
 p i
 r r
esentationisnotat

Notes

• The string will only consist of characters from a to z.
• Leading/Trailing whitespaces and newlines are allowed as long as the shape is not broken.
• A list of strings as output is allowed.

This is code-golf. Shortest answer in bytes wins. Standard loopholes apply.

Answer 1

Charcoal, (削除) 25 (削除ここまで) (削除) 22 (削除ここまで) 21 bytes

≔÷Lθ4λ↙...θλ→✂θλ±λ↖✂θ±λ

Try it online! Link is to verbose version of code. Simply slices the string into three parts and prints them in the appropriate directions. Edit: Saved 3 bytes by using integer division and slicing. Saved a further byte by using CycleChop instead of Slice for the head of the string. Edit: Charcoal now supports drawing arbitrary text along the edge of a polygon, simplifying the code to 12 bytes:

GH↙→→↖⊕÷Lθ4θ

Try it online! Link is to verbose version of code.

• Erik the Outgolfer: What do the ✂s do?
• Neil: @EriktheOutgolfer That's the new Slice operator.
• ASCII-only: :| Oops meant to make PolygonHollow do this, GH↙→→↖⊕÷Lθ4θ will work next time I push Charcoal

Answer 2

05AB1E, 23 bytes

ćsIg4÷GćsÁćsŠN·<ú«s}».C

Try it online!

Explanation

ć # extract head of input
 s # swap the remaining string to top of stack
 Ig4÷G # for N in [1...len(input)/4-1] do:
 ć # extract head
 sÁ # swap remaining string to top of stack and rotate right
 ć # extract head
 sŠ # reorder stack as tail, head, remaining
 N·<ú # prepend N-1 spaces to tail
 «s # concatenate with head and swap remaining string to top
 } # end loop
 ».C # join by newlines and center

Answer 3

JavaScript (ES6), (削除) 119 (削除ここまで) (削除) 117 (削除ここまで) (削除) 108 (削除ここまで) 105 bytes

s=>(l=s.length/4,S=' ',g=([c,...s],p)=>S.repeat(l)+c+(l--?p+s.pop()+`
`+g(s,p?p+S+S:S):s.join``))(s+S,'')

Formatted and commented

s => ( // given the input string s:
 l = s.length / 4, // l = length of side edge - 1
 S = ' ', // S = space (defining S costs 6 bytes but saves 7)
 g = ( // g = recursive function which takes:
 [c, // - c = next character
 ...s], // - s = array of remaining characters
 p) => // - p = middle padding string
 S.repeat(l) + c + ( // append left padding + left character
 l-- ? // if side edges are not complete:
 p + s.pop() + '\n' + // append middle padding + right character + Line Feed
 g(s, p ? p + S + S : S) // and do a recursive call with updated middle padding
 : // else:
 s.join`` // append all remaining characters and stop recursion
 ) // (this is the bottom edge)
 )(s + S, '') // initial call to g()

Test cases

let f =
s=>(l=s.length/4,S=' ',g=([c,...s],p)=>S.repeat(l)+c+(l--?p+s.pop()+`
`+g(s,p?p+S+S:S):s.join``))(s+S,'')
console.log(f('abcdefghijkl'))
console.log(f('iamastringwithalengthdivisiblebyfour'))
console.log(f('thisrepresentationisnotatriangle'))

Answer 4

C#, 260 bytes

namespace System{using static Console;class P{static void Main(){var d=ReadLine();int e=d.Length/4,x=e,y=0,g=0,i=0;Action<int,int>a=(p,q)=>{SetCursorPosition(p,q);Write(d[g++]);};for(;i<e;i++)a(x--,y++);for(i=0;i<e*2;i++)a(x++,y);for(i=0;i<e;i++)a(x--,y--);}}}

Really wanted to use SetCursorPosition.

Ungolfed:

namespace System {
 using static Console;
 class P {
 static void Main() {
 var d = ReadLine();
 int e = d.Length / 4, x = e, y = 0, g = 0, i = 0;
 Action<int, int> a = (p, q) => { SetCursorPosition(p, q); Write(d[g++]); };
 for (; i < e; i++)
 a(x--, y++);
 for (i = 0; i < e * 2; i++)
 a(x++, y);
 for (i = 0; i < e; i++)
 a(x--, y--);
 }
 }
}

• confusedandamused: Pardon my ignorance, but what is the purpose of Action in your solution? Is it just less bytes than a void function?
• LiefdeWen: @confusedandamused I'm used to writing single function answers so didn't even consider putting the function normally, it will be shorter though.

Answer 5

Mathematica, 164 bytes

(b=Length[c=Characters@#];k=Column[#,Alignment->Center]&;T=Table;k@{#&@@c,k@T[""<>{c[[i+2]],T[" ",2i+1],c[[-i-1]]},{i,0,(a=b/4)-2}],""<>T[c[[i]],{i,a+1,b/2+1+a}]})&

input

["iamastringwithalengthdivisiblebyfour"]

• user202729: We all know that [[1]] can be replaced with #&@@.
• ZaMoC: you are all so smart sweeties!
• user202729: I meant codegolf.stackexchange.com/questions/12900/… .
• Martin Ender: When you find yourself doing @(...), just do [...] instead. And I haven't tested but you can probably save another byte by giving Column a name (or maybe even to Column[#,Alignment->Center]& to avoid q) and then by putting all the remaining variables into the first argument of the outer Column (to save the surrounding parentheses).

Answer 6

Python 3, 120 bytes

First golf, figured I might as well learn some Python along the way.

a=input()
l=len(a)//4
print(l*" "+a[0])
for i in range(1,l):print((l-i)*" "+a[i]+(2*i-1)*" "+a[4*l-i])
print(a[l:3*l+1])

Try it online!

Explanation:

The first character is printed by itself after len(a)//4 spaces, then the first and last i-th characters starting from the second are printed, separated by 2*i - 1 spaces.

Finally, the remaining substring is printed.

• Leaky Nun: Welcome to PPCG! You can learn from this solution.
• FlipTack: A possible golf here is to declare p=print, and then simply use p for the three prints you use.
• FlipTack: Also, as the string length is guaranteed to always be divisible by four, // (floor division) can be replaced with /.
• FlipTack: By the way, the code you've linked to try online is not the same as the code in your answer.

Answer 7

GNU sed, (削除) 178 (削除ここまで) (削除) 158 (削除ここまで) 132 + 1 = 133 bytes

+1 byte for -r flag.

s/(.)(.*)(.)/ 1円\n2円;3円/
:
s/( *)(.\n.)(.*)(...);(.*)(.)/1円2円1円 6円\n3円;4円5円/m
t
:A
s/(.*\n)( *)(.*);/ 2円;1円2円3円/m
tA
s/. (.)$/1円/gm

Try it online!

Explanation

In previous revisions I used a lot of bytes dealing with math, special cases, and cleanup, even though intuitively I was sure they could be avoided. I've since managed to do so, mostly.

Suppose we have the input abcdEFGHIJKLMnop. The letters EFGHIJKLM will be the bottom of the triangle, so I've capitalized them as a visual aid.

First we prepare the input by putting the first character on its own line (preceded by a space) and inserting a cursor (;) before the last character:

s/(.)(.*)(.)/ 1円\n2円;3円/

Now we have:

 a
bcdEFGHIJKLMno;p

Now, in a loop, we're going to do a few things to the last line: 1. Copy the spaces from the previous line and insert them after the first character, plus two; 2. Move the last character to right after the spaces, followed by a newline; and 3. Move the cursor three characters to the left.

:
 s/( *)(.\n.)(.*)(...);(.*)(.)/1円2円1円 6円\n3円;4円5円/m
 t

Here's the result of each iteration:

 a
b p
cdEFGHIJKL;Mno
 a
b p
c o
dEFGHI;JKLMn
 a
b p
c o
d n
EF;GHIJKLM

You can see the pyramid begin to take shape. You can also see what the cursor was for: In each iteration it moved left three characters, and when there are no longer three characters to its left, it breaks the loop, which happens to be just when we've reached the "bottom" of the pyramid.

Now we're going to do a similar operation but in reverse. In a loop, we'll copy the spaces from the beginning of the line with the cursor to the beginning of the preceding line, plus one, in the process moving the cursor up to that line.

:A
 s/(.*\n)( *)(.*);/ 2円;1円2円3円/m
 tA

Here are a couple iterations and the end result:

 a
b p
c o
 ;d n
EFGHIJKLM
 a
b p
 ;c o
 d n
EFGHIJKLM
...
 ; a
 b p
 c o
 d n
EFGHIJKLM

We're all done now, except for some extra characters: A ; and extra space on the first line, and two spaces in the "middle" of the pyramid on the next three lines. A simple substitution gets rid of them:

s/. (.)$/1円/gm

All done!

 a
 b p
 c o
 d n
EFGHIJKLM

Answer 8

Haskell, 136 bytes

i#x=x<$[1..i]
f s|let h=div l 4;l=length s=unlines$[(h-i)#' '++(s!!i):(2*i-1)#' '++[(s++" ")!!(l-i)]|i<-[0..h-1]]++[drop h$take(l-h+1)s]

Try it online!

Answer 9

Ruby, 106 bytes

i=-1
s= ~/$/
sub /./,"#{' '*l=s/4}\0円
"
(l-1).times{sub /^(\w)(.*)(.)/,"#{' '*l-=1}\1円#{' '*i+=2}\3円
\2円"}

Try it online!

Answer 10

Python 2, (削除) 100 97 (削除ここまで)96 bytes

• Jacoblaw saved 1 byte: integer division is unnecessary

a=input()+" "
k=j=len(a)/4
while j:print j*" "+a[0]+(2*(k-j)-1)*" "+a[-1];a=a[1:-1];j-=1
print a

Try it online!

Explanation:

One smart thing I've done here is padded the input with a space at the end, such that the first character pairs with it and this can be pushed into the loop (and since trailing whitespaces are allowed)

abcdefghijkl[space] 
To print [0] [-1] Output=>[spaces]a[another_calculated_spaces(=0 here)][space]
Strip at both ends(a[1:-1]) 
bcdefghijkl 
To print [0] [-1] Output=>[spaces]b[another_calculated_spaces]l
Strip at both ends(a[1:-1])
and so on.

The number of loops to follow is associated with len(word)//4. In the final step, the whole remaining string is printed(this forms the base of the triangle). The spaces follow a simple pattern; the first set of spaces go-on decreasing by 1, while second set of spaces go on increasing by 2.

• jacoblaw: Can you shave off a byte by not doing integer division? Since a will always be a multiple of 4. // -> /
• 0xffcourse: Thank you, I am surprised it is not throwing any errors even for [inputs with length not divisible by 4] [tio.run/…
• CalculatorFeline: That's because in Python 2, division is integer by default. That was canged in Python 3.

Answer 11

C 225 bytes

p(c){putchar(c);}S(n){while(n--)p(' ');}main(int c,char**v){int i= strlen(v[1]),n=i/4,r;char*s=v[1],*e=&s[i-1];S(n);p(*s++);p('\n');for (r=1;r<n;r++){S(n-r);p(*s++);S(2*r-1);p(*e--);p('\n');}e++;while (s!=e)p(*s++);p('\n');}

explained

p(c){putchar(c);} // p is alias for putchar
S(n){while(n--)p(' ');} // S prints n spaces
main(int c,char**v){
 int i= strlen(v[1]), // counter
 n=i/4, // num rows in figure - 1
 r; // current row 
 char*s=v[1], // start char
 *e=&s[i-1]; // end char
 S(n);p(*s++);p('\n');// print first row
 for (r=1;r<n;r++){ 
 S(n-r);p(*s++);S(2*r-1);p(*e--);p('\n'); // print middle rows
 }
 e++;while (s!=e)p(*s++);p('\n'); // print last row
}

• ceilingcat: 163 bytes

Answer 12

C#, 172 bytes

int i=0,n=s.Length;var p="";p=new string(' ',n/4)+s[i]+"\r\n";for(i=1;i<n/4;i++){p+=new string(' ',n/4-i)+s[i]+new string(' ',i*2-1)+s[n-i]+"\r\n";}p+=s.Substring(i,n/2+1);

Try it online!

Answer 13

Octave, 87 bytes

@(s,x=(n=nnz(s))/4)[[' ';flip(diag(s(1:x))')]' [' ';diag(s(n:-1:n-x+2))];s(x+1:n-x+1)];

*In a windows machine the above code produces the correct result however in tio I added some code to correct it.

Explanation:

[' ';flip(diag(s(1:x))')]' %left side
[' ';diag(s(n:-1:n-x+2))] %right side
s(x+1:n-x+1) %bottom side

Try it online!

Answer 14

PHP>=7.1, 122 Bytes

for(;$i*2<$w=strlen($a=$argn)/2;$e=$a[-++$i])echo str_pad(str_pad($a[$i],$i*2).$e,$w+1," ",2),"
";echo substr($a,$i,$w+1);

PHP Sandbox Online

PHP>=7.1, 124 Bytes

for(;$i*2<$w=strlen($a=$argn)/2;$e=$a[-++$i],$s.=$s?" ":" ")echo str_pad("",$w/2-$i)."$a[$i]$s$e
";echo substr($a,$i,$w+1);

PHP Sandbox Online

Answer 15

AWK, 129 bytes

{n=split(0,ドルa,"")
printf"%"(w=n/4+1)"s\n",a[++i]
for(;++i<w;)printf"%"(w-i+1)"s%"2*i-2"s\n",a[i],a[n-i+2]
0ドル=substr(0,ドルi,i+w-1)}1

Try it online!

I should think this could be golfed a bit more, just not seeing it.

Answer 16

Retina, 99 bytes

^(.)(?=(....)+)
$#2$* 1ドル¶$#2$* 
( ( *).)(.*)(.)$
1ドル 4ドル¶2ドル3ドル
+`(( +).¶ ( *).)(.*)(.)$
1ドル2ドル 5ドル¶3ドル4ドル

Try it online! Explanation: The first two stages generate the first two lines, but after that no special-casing is necessary and each subsequent line can be generated automatically:

thisrepresentationisnotatriangle
 t
 hisrepresentationisnotatriangle
 t
 h e
 isrepresentationisnotatriangl
 t
 h e
 i l
 srepresentationisnotatriang
...
 t
 h e
 i l
 s g
 r n
 e a
 p i
 r r
esentationisnotat

Answer 17

Java 11, (削除) 213 (削除ここまで) (削除) 211 (削除ここまで) 178 bytes

s->{int n=s.length()/4,i=1;var r=" ".repeat(n)+s.charAt(0)+"\n";for(;i<n;r+=" ".repeat(n-i)+s.charAt(i)+" ".repeat(i*2-1)+s.charAt(n*4-i++)+"\n");return r+s.substring(i,n*2-~i);}

-2 bytes thanks to @ceilingcat.

Explanation:

Try it online.

s->{ // Method with String parameter and String return-type
 int n=s.length()/4, // The length of the input divided by 4
 i=1; // And an index-integer, starting at 1
 var r= // Result-String which starts as:
 " ".repeat(n) // Leading spaces
 +s.charAt(0) // + the first character
 +"\n"; // + a new-line
 for(;i<n; // Loop `i` in the range [1, `n`):
 r+= // And append the result-String with:
 " ".repeat(n-i) // Leading spaces
 +s.charAt(i) // + the character of the left diagonal line
 +" ".repeat(i*2-1) // + center spaces
 +s.charAt(n*4-i++) // + the character of the right diagonal line
 +"\n"); // + a new-line
 return r // Return the result-String
 +s.substring(i,n*2+i+1);} // + the bottom part of the triangle

• Kevin Cruijssen: @ceilingcat Thanks, pretty stupid mistake, haha. I've been able to golf it some more by using Java 11's " ".repeat(n) and Java 10's var instead of that separated method and String.

Answer 18

Vyxal C, 29 bytes

4/÷ḣ‟+^ṘYṘ2ẇṘḣð£ƛ\j\ðd+£;J^JJ

Try it Online!

No canvas builtins! Because Vyxal doesn't have those. feature-request?

-9 thanks to Aaron Miller.

• Aaroneous Miller: 29 bytes

Answer 19

Perl 5, 76 bytes

74 bytes of code +2 for -F

say$"x($l=@F/4),shift@F;say$"x$l,shift@F,$"x($#i+=2),pop@F while--$l;say@F

Try it online!

Answer 20

05AB1E, 14 bytes

g4/>x<‚ĆI527SΛ

Try it online (no test suite since there isn't a way to clean the Canvas).

Explanation:

g # Take the length of the (implicit) input
 # i.e. "thisrepresentationisnotatriangle" → 32
 4/ # Divide it by 4
 # i.e. 32 → 8
 > # Increase it by 1
 # i.e. 8 → 9
 x # Double it (without popping the value itself)
 # i.e. 9 → 9 and 18
 < # Decrease this doubled value by 1
 # i.e. 18 → 17
 ‚ # Pair them together: [length/4+1, (length/4+1)/2-1]
 # i.e. 9 and 17 → [9,17]
 Ć # Enclose it, appending its head to itself: [l/4+1, (l/4+1)/2-1, l/4+1]
 # i.e. [9,17] → [9,17,9]
I # Push the input-string again
527S # Push 527 as digit-list: [5,2,7]
Λ # Use the Canvas builtin with these three arguments
 # (after which the result is output implicitly)

Canvas explanation:

The Canvas builtin takes three arguments:
1. The lengths of the lines to 'draw', which in this case is the list \$[\frac{l}{4}+1, \frac{\left(\frac{l}{4}+1\right)}{2}-1, \frac{l}{4}+1]\$.
2. The string to 'draw', which in this case is the input. 3. The directions, which in this case is [5,2,7]. These will be the directions [↙,→,↖].

With these arguments, it will draw as follows (let's take the string "thisrepresentationisnotatriangle" as example again):

9 characters ("thisrepre") in direction 5 (↙)
 t
 h 
 i 
 s 
 r 
 e 
 p 
 r 
e 
17-1 characters ("sentationisnotat") in direction 2 (→):
 t 
 h 
 i 
 s 
 r 
 e 
 p 
 r 
esentationisnotatr
9-1 characters ("riangle") in direction 7 (↖):
(NOTE: "riangle" are only 7 characters instead of 8, since the string isn't any longer,
 which won't cause problems and is actually convenient for our desired output)
 t 
 h e 
 i l 
 s g 
 r n 
 e a 
 p i 
 r r 
esentationisnotat

See this 05AB1E tip of mine for a more in-depth explanation of the Canvas builtin.