32
\$\begingroup\$

I once had a beautiful rectangular array. It was very symmetrical, but unfortunately it has fallen apart and now I only have the top left corner. Your task will be to rebuild the original array.

Your program will receive a 2 dimensional array of integers. For ease of parsing, you may assume they are all between 1 and 9. Your task is to reverse the array's columns, its rows, and both, stitch together the resulting corners, and return the resulting array.

You can assume the array dimensions will be at least 1x1.

Test cases:

Input:
1 2 3
4 5 6

Output:
1 2 3 3 2 1
4 5 6 6 5 4
4 5 6 6 5 4
1 2 3 3 2 1

Input:
1

Output:
1 1
1 1

Input:
9
9
9

Output:
9 9
9 9
9 9
9 9
9 9
9 9

This is , fewest bytes wins!

\$\endgroup\$
9
  • 1
    \$\begingroup\$ I'll bet charcoal can do this in under 10 \$\endgroup\$
    – qqq
    Mar 5, 2018 at 16:19
  • 1
    \$\begingroup\$ @tbfninja chat.stackexchange.com/transcript/message/43184083#43184083 but could maybe be shorter with a different input format. \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 16:20
  • \$\begingroup\$ @MagicOctopusUrn yes \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 16:39
  • 2
    \$\begingroup\$ @tfbninja WS⟦ι⟧‖M→↓ perhaps? 5 bytes to read the input and 4 to reflect it. \$\endgroup\$
    – Neil
    Mar 5, 2018 at 17:51
  • 4
    \$\begingroup\$ I'm 99% sure that there is a lang that do this with (or some similar character) just can't remember which one :c \$\endgroup\$
    – Rod
    Mar 5, 2018 at 19:36

34 Answers 34

19
\$\begingroup\$

Canvas, 1 byte

Try it here!

Outputs as a multiline string

\$\endgroup\$
3
  • 2
    \$\begingroup\$ Nice, @Rod called that one hah! Is this your language too Dzaima? \$\endgroup\$ Mar 5, 2018 at 20:49
  • \$\begingroup\$ Damn... I should've remembered... \$\endgroup\$ Mar 5, 2018 at 20:53
  • \$\begingroup\$ @MagicOctopusUrn Yeah, IIRC it's meant to basically be S.O.G.L. II: Electric Boogaloo? \$\endgroup\$
    – ASCII-only
    Mar 6, 2018 at 10:50
12
\$\begingroup\$

Haskell, 25 24 bytes

r=(++)<*>reverse
r.map r

Try it online!

\$\endgroup\$
5
\$\begingroup\$

Python 3, 38 bytes

lambda a:[b+b[::-1]for b in a+a[::-1]]

Try it online!

Takes a list of lists and returns a list of lists.

Explanation:

lambda a:                              # anonymous lambda function
                   for b in a+a[::-1]  # for each row in the array and the upside-down array
          b+b[::-1]                    # the row with its reverse appended
         [                           ] # return in a list
\$\endgroup\$
5
\$\begingroup\$

Husk,  7  6 bytes

Coincidentally, Erik had posted the exact same code in the Husk chatroom about a minute before I posted this.

‼oTS+↔

Try it online!

Pervious version, 7 bytes:

mS+↔S+↔
\$\endgroup\$
5
\$\begingroup\$

Retina, 13 bytes

\%`$
$^$`
Vs`

Try it online!

Explanation

\%`$
$^$`

On each line (%), match the end of the line ($), and insert the reverse ($^) of the entire line ($`) and print the result with a trailing linefeed (\). This does the reflection along the vertical axis and prints the first half of the output.

Vs`

This just reverses the entire string, which is equivalent to a 180° degree rotation, or in our case (due to the horizontal symmetry) a reflection along the horizontal axis. This way this works is that V's (reverse) default regex is (?m:^.*$), which normally matches each line of the string. However, we activate the singleline option s, which makes . match linefeeds as well and therefore this default regex actually matches the entire string.

The result of this is printed automatically at the end of the program, giving us the second half of the output.

\$\endgroup\$
3
  • \$\begingroup\$ This doesn't look like any regex flavor I know of :P \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 16:36
  • \$\begingroup\$ @Pavel Because Retina isn't just regex. :) \$\endgroup\$ Mar 5, 2018 at 16:36
  • \$\begingroup\$ @Pavel the only part of that code that is an actual regex is the $ on the first line. ;) I'll add an explanation later. \$\endgroup\$ Mar 5, 2018 at 17:01
5
\$\begingroup\$

05AB1E, 2 bytes

∞∊

Try it online!


   # Input:Array of String | ['12','34']
---#-----------------------+------------------------------------------
∞  # Mirror horizontally.  | [12,34]       -> [1221,3443]
 ∊ # Mirror vertically.    | [1221,3443]   -> [1221\n3443\n3443\n1221]

Credit for Mr. Xcoder pointing out that arrays of string may count as 2D arrays and Pavel for confirming it.

\$\endgroup\$
5
  • \$\begingroup\$ ... 2 bytes \$\endgroup\$
    – Mr. Xcoder
    Mar 5, 2018 at 16:35
  • \$\begingroup\$ For ease of parsing, you may assume they are all between 1 and 9 – So I think this is valid. Awaiting Pavel's confirmation, I guess \$\endgroup\$
    – Mr. Xcoder
    Mar 5, 2018 at 16:37
  • \$\begingroup\$ @Mr.Xcoder that was what I had initially, then the TIO 2D arrays as input was weird... so had to come up with that header stuff. \$\endgroup\$ Mar 5, 2018 at 16:38
  • \$\begingroup\$ A string is an array of characters, so a list of strings is still a 2d array. @Mr.Xcoder's solution is valid. \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 16:38
  • \$\begingroup\$ Coolio, works for me. \$\endgroup\$ Mar 5, 2018 at 16:41
3
\$\begingroup\$

Jelly, 5 bytes

m€0m0

Try it online!

\$\endgroup\$
1
  • \$\begingroup\$ Also 5 bytes: m0Z$⁺ (by Hyper Neutrino). \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 16:05
3
\$\begingroup\$

MATL, 5 bytes

,tPv!

Try it online!

Explanation:

(implicit input)
,               # do twice:
 t              # dup top of stack
 P              # flip vertically
 v              # vertically concatenate
 !              # transpose
(implicit output)

\$\endgroup\$
3
\$\begingroup\$

Octave,  33  29 bytes

Thanks to @Giuseppe for golfing four bytes!

@(A)[B=[A;flip(A)] fliplr(B)]

Try it online!

\$\endgroup\$
1
3
\$\begingroup\$

Ruby, 35 bytes

->a{r=->b{b+b.reverse}
r[a].map &r}

Try it online!

A lambda accepting a 2D array and returning a 2D array. It's straightforward, but here's the ungolfed version anyway:

->a{
  r=->b{ b+b.reverse } # r is a lambda that returns the argument and its reverse
  r[a].map &r          # Add the array's reverse, then add each row's reverse
}
\$\endgroup\$
3
\$\begingroup\$

JavaScript (Node.js), 62 55 49 46 bytes

A=>(j=x=>[...x,...[...x].reverse()])(A).map(j)

Try it online!

Because Array.prototype.reverse() reverses the array in place, I have to make a shallow copy somewhere first. A=>(j=x=>[...x,...x.reverse()])(A).map(j) does not work.

\$\endgroup\$
3
\$\begingroup\$

J, 12 bytes

(,|.)@,.|."1

Try it online!

Explanation

         |."1 - reverse each row
       ,.     - and stitch them to the input
 (   )@       - and 
  ,|.         - append the rows in reversed order        
\$\endgroup\$
3
\$\begingroup\$

awk, 88 bytes

{s="";for(i=NF;i>0;i--)s=" "$i s" "$i;a[FNR]=s;print s}END{for(i=NR;i>0;i--)print a[i]}
\$\endgroup\$
1
  • 3
    \$\begingroup\$ Welcome to PPCG! Nice first answer :) \$\endgroup\$
    – hyper-neutrino
    Mar 8, 2018 at 15:34
2
\$\begingroup\$

Triangularity, 31 bytes

...)...
..IEM..
.DRs+}.
DRs+...

Try it online!

Explanation

Removing the characters that make up for the padding, here is what the program does:

)IEMDRs+}DRs+ – Full program. Takes a matrix as a 2D list from STDIN.
)             – Push a 0 onto the stack.
 I            – Take the input at that index.
  E           – Evaluate it.
   M    }     – For each row...
    DR        – Duplicate and replace the second copy by its reverse.
      s+      – Swap and append.
         DR   – Duplicate the result and replace the second copy by its reverse.
           s+ – Swap and append.
\$\endgroup\$
2
\$\begingroup\$

R, 57 bytes

function(m)rbind(N<-cbind(m,m[,ncol(m):1]),N[nrow(N):1,])

Try it online!

\$\endgroup\$
2
\$\begingroup\$

APL+WIN, 11 bytes

Prompts for a 2d array of integers.

m⍪⊖m←m,⌽m←⎕
\$\endgroup\$
2
\$\begingroup\$

Stax, 5 bytes

:mm:m

Run and debug it online

:m means mirror, which is input.concat(reverse(input)). m, in this context means output each line after applying...

So, mirror the array of rows, and then mirror each row and output.

\$\endgroup\$
0
2
\$\begingroup\$

Japt, 6 bytes

mê1 ê1

Try it here


Explanation

           :Implicit input of 2D array
m          :Map
 ê1        :  Mirror sub array
    ê1     :Mirror main array
\$\endgroup\$
2
\$\begingroup\$

Mathematica, 29 bytes

(g=#~Join~Reverse@#&)@*Map[g]

Try it online!

\$\endgroup\$
2
\$\begingroup\$

SOGL V0.12, 2 bytes

-1 byte thanks to dzaima.

╬ø

Try it here!

\$\endgroup\$
0
2
\$\begingroup\$

APL (Dyalog Classic), 7 bytes

⍪∘⊖⍨⊢,⌽

Try it online!

\$\endgroup\$
2
\$\begingroup\$

Java 8, 140 131 bytes

m->{String r="";for(int a=m.length,b=m[0].length,i=a+a,j;i-->0;r+="\n")for(j=b+b;j-->0;)r+=m[i<a?i:a+a+~i][j<b?j:b+b+~j];return r;}

Explanation:

Try it online.

m->{                      // Method with integer-matrix parameter and String return-type
  String r="";            //  Result-String, starting empty
  for(int a=m.length,     //  Amount of rows of the input-matrix
          b=m[0].length,  //  Amount of columns of the input-matrix
          i=a+a,j;        //  Index integers
      i-->0;              //  Loop over double the rows
      r+="\n")            //    After every iteration: append a new-line to the result
     for(j=b+b;j-->0;)    //   Inner loop over double the columns
       r+=                //    Append the result with:
          m[i<a?          //     If `i` is smaller than the amount of rows
             i            //      Use `i` as index in the input-matrix
            :             //     Else:
             a+a+~i]      //      Use `a+a+i-1` as index instead
           [j<b?          //     If `j` is smaller than the amount of columns
             j            //      Use `j` as index in the input-matrix
            :             //     Else:
             b+b+~j];     //      Use `b+b+j-1` as index instead
  return r;}              //  Return the result-String
\$\endgroup\$
2
\$\begingroup\$

J, 11 bytes

Anonymous tacit prefix function.

|:@(,|.)^:2

Try it online!

|: transpose

@(…) the result of:

, the argument followed by

|. its reverse

^:2 and all this done twice

\$\endgroup\$
2
\$\begingroup\$

SNOBOL4 (CSNOBOL4), 119 113 bytes

	T =TABLE()
I	X =X + 1
	I =INPUT	:F(D)
	OUTPUT =T<X> =I REVERSE(I)	:(I)
D	X =X - 1
	OUTPUT =GT(X) T<X>	:S(D)
END	

Try it online!

Takes input as strings on STDIN, without spaces. This only works because the digits are 1-9 and would fail otherwise.

\$\endgroup\$
2
  • \$\begingroup\$ I can see why people don't use this language anymore. This is so weird. \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 17:15
  • 1
    \$\begingroup\$ @Pavel SNOBOL is truly a terrible language to work with. this is a more modern C implementation of it which has additional builtin functions like REVERSE; the original only supported integer arithmetic as well, as far as I can tell. \$\endgroup\$
    – Giuseppe
    Mar 5, 2018 at 17:29
2
\$\begingroup\$

C (gcc), 114 111 bytes

j,i;f(A,w,h)int*A;{for(i=h+h;i-->0;puts(""))for(j=w+w;j-->0;)printf("%d,",A[(i<h?i:h+h+~i)*w+(j<w?j:w+w+~j)]);}

Try it online!

C (gcc), 109 bytes (abusing ease of parsing)

  • Thanks to Kevin Cruijssen for suggesting to only allow one-digit input integers; saved two bytes.
j,i;f(A,w,h)int*A;{for(i=h+h;i-->0;puts(""))for(j=w+w;j-->0;)putchar(A[(i<h?i:h+h+~i)*w+(j<w?j:w+w+~j)]+48);}

Try it online!

\$\endgroup\$
5
  • \$\begingroup\$ You can save 3 bytes by inverting the loops. for(i=h+h;i-->0;puts(""))for(j=w+w;j-->0;) \$\endgroup\$ Mar 6, 2018 at 8:18
  • \$\begingroup\$ Does not fulfill spec; prints the array, rather than returning it. \$\endgroup\$
    – user77406
    Mar 6, 2018 at 11:14
  • \$\begingroup\$ "For ease of parsing, you may assume they are all between 1 and 9.", so you can remove the comma in the printf("%d" for an additional -1 byte. \$\endgroup\$ Mar 6, 2018 at 15:12
  • \$\begingroup\$ @Rogem I would say printing the array falls under accepted i/o. \$\endgroup\$ Mar 6, 2018 at 19:07
  • 1
    \$\begingroup\$ @KevinCruijssen Thanks a lot; using the ease of parsing I managed to shave off another byte. \$\endgroup\$ Mar 6, 2018 at 19:12
2
\$\begingroup\$

Charcoal, 5 bytes

θ‖C→↓

Try it online!

Thanks to ASCII-only for a better input format.

\$\endgroup\$
9
  • \$\begingroup\$ I wonder if this input format is valid, since I'm afraid Charcoal can't handle input otherwise. If it isn't, I'll happily delete this answer. \$\endgroup\$ Mar 5, 2018 at 18:41
  • \$\begingroup\$ This is valid I/o. \$\endgroup\$
    – Pavel
    Mar 5, 2018 at 18:42
  • \$\begingroup\$ @Pavel I just wondered because you had said that "Your program will receive a 2 dimensional array of integers", while a string is 1-dimensional (and no, the outer [] don't exactly make it 2D). \$\endgroup\$ Mar 5, 2018 at 18:44
  • \$\begingroup\$ @ASCII-only Charcoal really needs a better I/O method... \$\endgroup\$
    – Neil
    Mar 5, 2018 at 20:09
  • \$\begingroup\$ @Neil He didn't get pinged here, but I pinged him over TNB. :) \$\endgroup\$ Mar 5, 2018 at 20:13
2
\$\begingroup\$

Add++, 30 bytes

D,f,@,bU€{r}B]{r}
D,r,@,dbR+

Try it online!

The footer simply transforms the nested array into the format in the question. Defines a function f, which expects a matrix (nested array) as an argument.

\$\endgroup\$
2
\$\begingroup\$

Uiua, 9 bytes

⍥(⍉⊂∶⇌.)2

Try it!

⍥(⍉⊂∶⇌.)2
⍥(     )2  # run a function twice
      .    # duplicate
     ⇌     # reverse
   ⊂∶      # prepend
  ⍉        # transpose
\$\endgroup\$
1
\$\begingroup\$

Julia 0.6, 55 49 bytes

~i=i:-1:1
!x=[x x[:,~end];x[~end,:] x[~end,~end]]

Try it online!

~(i) is a function to create slice from i down to 1.
So ~end gives the slice end:-1:1

!(x) is the function to do the rebuilding of the array.

\$\endgroup\$
1
\$\begingroup\$

V, 12 bytes

yGæGPÎy$æ_|P

Try it online!

Explanation:

yG              " Yank every line
  æG            " Reverse the order of the lines
    P           " Paste what we yanked
     Î          " On every line:
      y$        "   Yank the whole line
        æ_      "   Reverse the whole line
          |     "   Move to the beginning of the line
           P    "   Paste what we yanked
\$\endgroup\$
0

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