Confusing Alphabet Staircase

Question

Given no input, output this interesting alphabet pattern in either case (the case has to be consistent) via an accepted output method:

A
AB
ACBC
ADBDCD
AEBECEDE
AFBFCFDFEF
AGBGCGDGEGFG
AHBHCHDHEHFHGH
AIBICIDIEIFIGIHI
AJBJCJDJEJFJGJHJIJ
AKBKCKDKEKFKGKHKIKJK
ALBLCLDLELFLGLHLILJLKL
AMBMCMDMEMFMGMHMIMJMKMLM
ANBNCNDNENFNGNHNINJNKNLNMN
AOBOCODOEOFOGOHOIOJOKOLOMONO
APBPCPDPEPFPGPHPIPJPKPLPMPNPOP
AQBQCQDQEQFQGQHQIQJQKQLQMQNQOQPQ
ARBRCRDRERFRGRHRIRJRKRLRMRNRORPRQR
ASBSCSDSESFSGSHSISJSKSLSMSNSOSPSQSRS
ATBTCTDTETFTGTHTITJTKTLTMTNTOTPTQTRTST
AUBUCUDUEUFUGUHUIUJUKULUMUNUOUPUQURUSUTU
AVBVCVDVEVFVGVHVIVJVKVLVMVNVOVPVQVRVSVTVUV
AWBWCWDWEWFWGWHWIWJWKWLWMWNWOWPWQWRWSWTWUWVW
AXBXCXDXEXFXGXHXIXJXKXLXMXNXOXPXQXRXSXTXUXVXWX
AYBYCYDYEYFYGYHYIYJYKYLYMYNYOYPYQYRYSYTYUYVYWYXY
AZBZCZDZEZFZGZHZIZJZKZLZMZNZOZPZQZRZSZTZUZVZWZXZYZ

Trailing spaces and newlines are acceptable, standard loopholes are disallowed, and this happens to be code-golf, so the shortest answer in bytes wins!

Answer 1

Jelly, 9 bytes

ØAjṪ$Ƥż¹Y

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How it works

ØAjṪ$Ƥż¹Y  Main link. No arguments.

ØA         Yield "ABCDEFGHIJKLMNOPQRSTUVWXYZ".
     Ƥ     Map the link to the left over all prefixes, i.e., ["A", "AB", ...].
    $        Combine the two links to the left into a chain.
   Ṫ           Tail; yield and remove the last letter of each prefix.
  j            Join the remainder, using that letter as separator.
      ż¹   Zip the resulting strings and the letters of the alphabet.
        Y  Separate the results by linefeeds.

Answer 2

C, 82 bytes

f(i,j){for(i=!puts("A");++i<26;puts(""))for(j=0;j++<i*2;)putchar(65+(j&1?j/2:i));}

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Answer 3

Charcoal, 9 bytes

Ｅα⁺⪫…ακιι

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

 α          Predefined uppercase alphabet
Ｅ           Map over each character
    …ακ     Get current prefix of alphabet
   ⪫   ι    Join with current character
  ⁺     ι   Append current character
            Implicitly print on separate lines

Answer 4

Canvas, 7 bytes

Ｚ［Ｋ＊¹＋］

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Explanation:

Ｚ［     ］ for each prefix of the uppercase alphabet
    Ｋ        pop off the last letter
     ＊       and join the rest of the string with that character
      ¹＋     and append the current iterated character to it

Answer 5

R, 50 bytes

l=LETTERS
for(i in 0:25)cat(l[0:i],"
",sep=l[i+1])

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Perhaps the cleverest part here is using letters[0] for the empty string to get cat(character(0),'\n',sep="A") to print the first line.

Answer 6

Python 2, 56 bytes

n=65;s='';exec'c=chr(n);print c.join(s)+c;s+=c;n+=1;'*26

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Answer 7

6502 machine code routine (C64), 39 bytes

A9 41 20 D2 FF AA A8 84 FB E4 FB B0 0B 8A 20 D2 FF 98 20 D2 FF E8 D0 F1 A9 0D
20 D2 FF A2 41 C0 5A F0 03 C8 D0 E1 60

Position-independet machine code subroutine, clobbers A, X and Y.

Online demo

The demo loads at $C000, so use SYS49152 to call the routine.

---

Commented disassembly:

A9 41       LDA #$41            ; 'A'
20 D2 FF    JSR $FFD2           ; Kernal CHROUT (output character)
AA          TAX                 ; copy to X (current pos)
A8          TAY                 ; copy to Y (current endpos)
  .outerloop:
84 FB       STY $FB             ; endpos to temporary
  .innerloop:
E4 FB       CPX $FB             ; compare pos with endpos
B0 0B       BCS .eol            ; reached -> do end of line
8A          TXA                 ; current pos to accu
20 D2 FF    JSR $FFD2           ; and output
98          TYA                 ; endpos to accu
20 D2 FF    JSR $FFD2           ; and output
E8          INX                 ; next character
D0 F1       BNE .innerloop      ; (repeat)
  .eol:
A9 0D       LDA #$0D            ; load newline
20 D2 FF    JSR $FFD2           ; and output
A2 41       LDX #$41            ; re-init current pos to 'A'
C0 5A       CPY #$5A            ; test endpos to 'Z'
F0 03       BEQ .done           ; done when 'Z' reached
C8          INY                 ; next endpos
D0 E1       BNE .outerloop      ; (repeat)
  .done:
60          RTS

Answer 8

Uiua 0.1.0 0.10.0, 21 bytes

∵(&p+@A♭≡⊂⇡.)⇡26&pf@A

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Answer 9

Java 8, 93 91 90 bytes

v->{String t="";for(char c=64;++c<91;t+=c)System.out.println(t.join(c+"",t.split(""))+c);}

-1 byte thanks to @OlivierGrégoire by printing directly instead of returning

Explanation:

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v->{                     // Method with empty unused parameter and String return-type
  String t="";           //  Temp-String, starting empty
  for(char c=64;++c<91;  //  Loop over the letters of the alphabet:
      t+=c)              //    After every iteration: append the letter to the temp-String
    System.out.println(  //   Print with trailing new-line:
       r.join(c+"",t.split(""))
                         //    The temp-String with the current letter as delimiter
       +c);}             //    + the current letter as trailing character 

Answer 10

SNOBOL4 (CSNOBOL4), 169 143 124 123 bytes

	L =LEN(1)
	OUTPUT ='A'
I	&UCASE (ARB K L) . R L . S :F(END)
	O =K =
T	R K L . K :F(O)
	O =O K S :(T)
O 	OUTPUT =O :(I)
END

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Explanation for older version of the code:

i &ucase len(x) . r len(1) . s	;* set r to the first x characters and s to the x+1th.
 o =				;* set o,i to empty string
 i =
t r len(i) len(1) . k :f(o)	;* set k to the ith letter of r. on failure (no match), go to o.
 o =o s k			;* concatenate o,s,k
 i =i + 1 :(t)			;* increment i, goto t
o o s =				;* remove the first occurrence of s (the first character for x>1, and nothing otherwise)
 output =o s			;* output o concatenated with s
 x =lt(x,25) x + 1 :s(i)	;* increment x, goto i if x<25.
end

The problem here is the first line

using o s k will add an extra separator character at the beginning of each line and also not have an s at the end. This is OK because line t will jump over the following two lines when x=0. This means that o will still be blank. Hence, o s = will remove the first s character from o, and then we can simply print o s to have the appropriate last s.

Answer 11

JavaScript (ES6), 81 bytes

f=
_=>[..."ABCDEFGHIJKLMNOPQRSTUVWXYZ"].map((c,i,a)=>a.slice(0,i).join(c)+c).join`
`
;document.write('<pre>'+f());

Save 9 bytes if a string array return value is acceptable.

Answer 12

PowerShell, 56 bytes

"A";65..89|%{([char[]](65..$_)-join[char]++$_)+[char]$_}

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Loops 65 to 89, each iteration constructing a char array of 65 to the current number $_, then -joins that array together into a string with the next character, then tacks on that character at the end.

Change the 89 to some other ASCII number to see the behavior better.

Answer 13

><>, 44 34 bytes

"BA"oao"ZA"\=?;1+40.
o1+:{::o}=?\:

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><>, 44 bytes

"A"o10ao\55*=?;1+40.
1+:{:}=?\:"A"+o{:}"A"+o

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As I use a different route to producing the output I've posted my own ><> answer; The other ><> answer can be found here.

Big thanks to Jo king for spotting I didn't need to keep putting "A" onto the stack if I just compared against "Z" instead of 26. (-10 bytes)

Explanation

The explanation will follow the flow of the code.

"BA"                 : Push "BA" onto the stack;
                       [] -> [66, 65]
    oao              : Print the stack top then print a new line;
                       [66, 65] -> [66]
       "ZA"\         : Push "ZA" onto the stack then move down to line 2;
                       [66, 90, 65]
o          \:        : Duplicate the stack top then print
 1+:                 : Add one to the stack top then duplicate;
                       [66, 90, 65, 65]
    {::              : Shift the stack right 1 place then duplicate the stack top twice;
                       [90, 65, 65, 66, 66]
       o}            : Print the stack top then shift the stack left 1 place;
                       [66, 90, 65, 65, 66]
         =?\         : Comparison for equality on the top 2 stack items then move to line 1 if equal otherwise continue on line 2;
                       [66, 90, 65]
           \=?;      : Comparison for equality on the top 2 stack items then quit if equal else continue on line 1;
                       [66]
               1+    : Add 1 to the stack top;
                       [67]
                 40. : Move the code pointer to column 4 row 0 of the code box and continue execution of code. 

Answer 14

Japt (-R flag), 14 12 bytes

-2 bytes thanks to @Shaggy

;B¬
ËiU¯E qD

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Answer 15

Acc!!, 84 bytes

This is actually what inspired this challenge:

Write 65
Count i while i-26 {
Count b while b-i {
Write b+65
Write i+65
}
Write 10
}

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Answer 16

Haskell, 49 48 bytes

'A':unlines[init['A'..x]>>=(:[x])|x<-['A'..'Z']]

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Edit: -1 byte thanks to totallyhuman!

Answer 17

C# (.NET Core)

Port from Kevin Cruijssen's answer:

91 90 bytes

_=>{var t="";for(char c='@';++c<91;t+=c)Console.WriteLine(string.Join(c+"",t.Skip(0))+c);}

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132 122 110 109 104 103 bytes

_=>"ABCDEFGHIJKLMNOPQRSTUVWXYZ".Select((c,i)=>string.Join(""+c,"ABCDEFGHIJKLMNOPQRSTUVWXYZ".Take(i))+c)

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• Replace () with _ to show that we declare an unused variable. Thank you Kevin Cruijssen.

Answer 18

Jelly, 22 bytes

ØAż€Ð€`F€µJ’Ḥ»1ż@¹ḣ/€Y

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How it works:

                       take argument implicitly
ØA                     the uppercase alphabet
    Ѐ`                for C in the alphabet
  ż€                     appends C to every letter in the alphabet
       F€              flatten every sublist
          J            get indices
           ’           subtract 1
            Ḥ          and double
             »1        take max([n, 1])
         µ     ż@¹     interleave alphabet list and indices
                  ḣ/€  reduce on head() for each element
                     Y join on newline
                       implicitly output

Answer 19

Ruby, 44 34 bytes

?A.upto(?Z){|w|puts [*?A...w]*w+w}

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Thanks benj2240 for getting it down to 37 bytes. And of course crossed out 44 blah blah.

Answer 20

05AB1E, 29 bytes

'A,Au©.sRí¦®RSDgÝ×Rs)ø˜.Bíø»=

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Answer 21

brainfuck, 96 bytes

+++++[->+++++>++>+++++++++++++>+++++++++++++<<<<]>>>.<.<[->>>+>+[-<<.+>.>>+<]>[-<+<<->>>]<<<<.<]

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Tape Layout:

[Init] [Line Count] [newline] [Growing Ascii] [Repeated Ascii] [Loop 1] [Loop 2]

Explanation:

+++++[->+++++>++                      Sets Line counter and newline cell
    >+++++++++++++>+++++++++++++<<<<] Sets Ascii cells to 65 ('A')
>>>.<.<                               Prints first "A" and moves to Line loop
  [->>>+>+                            Increment Repeated Ascii cell in outer loop
      [-<<.+>.>>+<]>                  Increment Growing Ascii cell in inner loop,
                                         Prints both Ascii cells and Sets Loop 2
      [-<+<<->>>]                     Resets Growing cell and Loop 1
  <<<<.<]                             Prints newline and moves to next Line

Answer 22

brainfuck, 81 bytes

+++[[->++<<+>]>]<<,<[----<<+>>]<+<+.<+<--.>[>+>>+[-<.+<.>>>+<]>[-<+<->>]<<<<<.>-]

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Prints in lowercase

Explanation:

+++[[->++<<+>]>]  Sets up the tape as 3*2^n (3,6,12,24,48,96,192,128)
<<,               Removes excess 128
<[----<<+>>]      Adds 196/4 to 48 resulting in 96
<+<+.             Add 1 to both 96s and print A
<+<--.            Add 1 to 25, subtract 2 from 12 to print a newline
                  Tape: 3 6 10 25 96 96 0 0
>[ Start loop
   >+>>+          Add one to the unchanging ASCII and the inner loop counter
   [-<.+<.>>>+<]  Print row while preserving counter
   >[-<+<->>]     Undo changes to changing ASCII and return inner loop counter to its cell
   <<<<<.>-       Print newline and decrement loop counter
]

Answer 23

brainfuck, 88 bytes

++++++++[->+++>+>++++++++>++++++++<<<<]>+>++>+.<.<[->>+>>+[-<+.<.>>>+<]>[-<+<->>]<<<<.<]

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should run on all brainfuck interpreters. No wrapping or negative values, no undefined input behaviour, values between 0 and 90.

How it works

Initialize tape: 25(row count) 10(lf) 64(row letter) 64(col letter) 0(col count) 0(temp)
++++++++[->+++>+>++++++++>++++++++<<<<]>+>++ 

>+.<.            print "A" and lf
<[               for each letter count
  -                decrement letter count
  >>+              increment row letter
  >>+              increment col count
  [                do col count times
    -                decrement col count
    <+.              increment and print col letter
    <.               print row letter
    >>>+             move col count to temp
    <                return to colcount
  ]
  >[-<+<->>]       move value from temp back to col count and set col letter back to "A" minus 1
  <<<<.            print lf
  <                return to row count
]

Answer 24

05AB1E, 12 bytes

AuηćsvyS¤ý¨»

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Explanation:

Au            # Push the uppercase alphabet
  η           # Pop and push its prefixes
   ć          # Extract the head; pop and push the remainder and head
    sv        # Loop `y` over each of the remainder prefixes:
      yS      #  Convert `y` to a list of characters
        ¤     #  Push it's last character (without popping)
         ý    #  Join the characters by this character
          ¨   #  Remove the last character of the string
           »  #  And join the entire stack by newlines
              # (after the loop, the result is output implicitly)

Answer 25

Deadfish~, 4152 bytes

{i}cc{iiiii}iiiiic{ddddd}dddddc{iiiii}iiiiicic{ddddd}ddddddc{iiiii}iiiiiciicdcic{dddddd}iiic{iiiii}iiiiiciiicddciicdcic{dddddd}iic{iiiii}iiiiiciiiicdddciiicddciicdcic{dddddd}ic{iiiii}iiiiiciiiiicddddciiiicdddciiicddciicdcic{dddddd}c{iiiii}iiiiiciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{dddddd}dc{iiiii}iiiiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{dddddd}ddc{iiiii}iiiiic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{dddddd}dddc{iiiii}iiiiic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{dddddd}ddddc{iiiii}iiiiic{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{dddddd}dddddc{iiiii}iiiiic{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{dddddd}ddddddc{iiiii}iiiiic{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}iiic{iiiii}iiiiic{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}iic{iiiii}iiiiic{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}ic{iiiii}iiiiic{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}c{iiiii}iiiiic{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}dc{iiiii}iiiiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}ddc{iiiii}iiiiic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}dddc{iiiii}iiiiic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}ddddc{iiiii}iiiiic{ii}c{dd}ic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}dddddc{iiiii}iiiiic{ii}ic{dd}c{ii}c{dd}ic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}iii}ddddddc{iiiii}iiiiic{ii}iic{dd}dc{ii}ic{dd}c{ii}c{dd}ic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}ii}iiic{iiiii}iiiiic{ii}iiic{dd}ddc{ii}iic{dd}dc{ii}ic{dd}c{ii}c{dd}ic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}ii}iic{iiiii}iiiiic{ii}iiiic{dd}dddc{ii}iiic{dd}ddc{ii}iic{dd}dc{ii}ic{dd}c{ii}c{dd}ic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}ii}ic{iiiii}iiiiic{ii}iiiiic{dd}ddddc{ii}iiiic{dd}dddc{ii}iiic{dd}ddc{ii}iic{dd}dc{ii}ic{dd}c{ii}c{dd}ic{ii}dc{dd}iic{ii}ddc{dd}iiic{ii}dddc{d}ddddddc{i}iiiiiic{d}dddddc{i}iiiiic{d}ddddc{i}iiiic{d}dddc{i}iiic{d}ddc{i}iic{d}dc{i}ic{d}c{i}c{d}ic{i}dc{d}iic{i}ddc{d}iiic{i}dddcddddddciiiiiicdddddciiiiicddddciiiicdddciiicddciicdcic{{d}ii}c

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Answer 26

Perl 5, 30 bytes

New method here shaves off a lot of the length.

say$,=A;say A..$,++,''for A..Y

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Old way: Perl 5, 39 38 bytes

@DomHastings shaved off a byte

say$.=A;say map$_.$.,A..$.++while$.!~Z

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Answer 27

Python 3, 77, 72, 67 bytes

# s=list(map(chr,list(range(65,91))))
# s='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
s=[*map(chr,range(65,91))]
for d in s:print(d.join(s[:ord(d)-65])+d)

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Just the @Chas-Brown Python 2 answer converted to Python 3.

Edit 1: 5 bytes saved thanks to @emanresu A!

Edit 2: more 5 bytes saved thanks to @Malo!

Answer 28

Jelly, 12 bytes

ØA;\;€Ṫ$€YFḊ

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Bah just got ØAjṪ$ƤżØAY which is a step between this and the already posted solution of Dennis :/

Answer 29

Pyth, 13 bytes

+\ajmPjedd._G

Try it here!, Alternative

That leading a though...

Answer 30

Jelly, 13 bytes

ØA¹Ƥ+"¹Ṗ€Yṭ”A

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Explanation

ØA¹Ƥ+"¹Ṗ€Yṭ”A  Main Link
ØA              Uppercase Alphabet
  ¹Ƥ            Prefixes
    +"¹         Doubly-vectorized addition to identity (uppercase alphabet) (gives lists of lists of strings)
       Ṗ€      a[:-1] of each (get rid of the double letters at the end)
         Y     Join on newlines
          ṭ”A  "A" + the result

partially abuses the way strings and character lists differ in Jelly