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Required fields*

Rev

Required fields*

Pointlessly make your way down the alphabet

Disclaimer: This challenge inspired by me spending the morning debugging recursive functions, which have been frying my brain a little.

Here's an example of recursion, from a letter, we keep going to the previous letter of the alphabet, printing out each one as we go, until we hit the letter a, then we print that and stop. We do this for each letter in a string and there's a pretty pattern at the end of it.

The task

Start with a string of characters
- The input string may only contain the lower-case letters a-z and the space character.
For each letter, produce a line of text (terminal output or variable or whatever)
- Print out the letter
- Print out the previous letter (on the same line)
- Print out the previous letter (on the same line)
- Print out the previous letter (on the same line)
- ...
- If the letter is 'a', print it out and move to the next line.
- If it's a space, print out an empty line (or one just containing the space character.

The rules

It's golf, try and make your code short.
Any language you like.
Please include a link to an online interpreter.
The output should be human-readable (e.g. I can't work it out from a list of bytes.
Follow the rules of the standard loopholes ̄\_(ツ)_/ ̄
Recursion is not mandated by the rules, but it's probably necessary.

Test Cases

Input: 'abcdefghijklmnopqrstuvwxyz' Output:

a
ba
cba
dcba
edcba
fedcba
gfedcba
hgfedcba
ihgfedcba
jihgfedcba
kjihgfedcba
lkjihgfedcba
mlkjihgfedcba
nmlkjihgfedcba
onmlkjihgfedcba
ponmlkjihgfedcba
qponmlkjihgfedcba
rqponmlkjihgfedcba
srqponmlkjihgfedcba
tsrqponmlkjihgfedcba
utsrqponmlkjihgfedcba
vutsrqponmlkjihgfedcba
wvutsrqponmlkjihgfedcba
xwvutsrqponmlkjihgfedcba
yxwvutsrqponmlkjihgfedcba
zyxwvutsrqponmlkjihgfedcba

Input: 'zyxwvutsrqponmlkjihgfedcba'

zyxwvutsrqponmlkjihgfedcba
yxwvutsrqponmlkjihgfedcba
xwvutsrqponmlkjihgfedcba
wvutsrqponmlkjihgfedcba
vutsrqponmlkjihgfedcba
utsrqponmlkjihgfedcba
tsrqponmlkjihgfedcba
srqponmlkjihgfedcba
rqponmlkjihgfedcba
qponmlkjihgfedcba
ponmlkjihgfedcba
onmlkjihgfedcba
nmlkjihgfedcba
mlkjihgfedcba
lkjihgfedcba
kjihgfedcba
jihgfedcba
ihgfedcba
hgfedcba
gfedcba
fedcba
edcba
dcba
cba
ba
a

Input: 'hello world' Output:

hgfedcba
edcba
lkjihgfedcba
lkjihgfedcba
onmlkjihgfedcba
wvutsrqponmlkjihgfedcba
onmlkjihgfedcba
rqponmlkjihgfedcba
lkjihgfedcba
dcba

Answer*

# Sed (with `-r` switch), <s>65</s> <s>61</s> <s>60</s> 59 characters

 s/./&zyxwvutsrqponmlkjihgfedcba \n/g
 s/(.).*1円/1円/gm
 s/ //g

Thanks to:

* [Kritixi Lithos](https://codegolf.stackexchange.com/users/41805/kritixi-lithos) for finding an unnecessary capturing (-3 characters)
* [Kritixi Lithos](https://codegolf.stackexchange.com/users/41805/kritixi-lithos) for <s>anchoring to line start</s> not anchoring instead of word start (<s>-1</s> 2 characters)
* [Kritixi Lithos](https://codegolf.stackexchange.com/users/41805/kritixi-lithos) for combining the 2 solutions advantages (2 characters)

Sample run:

 bash-5.0$ sed -r 's/./&zyxwvutsrqponmlkjihgfedcba \n/g;s/(.).*1円/1円/gm;s/ //g' <<< 'cg cc'
 cba
 gfedcba
 
 cba
 cba

[Try it online!](https://tio.run/##DcdLDkAwEADQvVN0JUh04j42aLVoO9XxP7wheZtHWjETSMif@zqPfaO0RgzeLfNkzajV0HeiDWAygkKWsmob@Bn/XwAYZqudE2jFicmpF@M2YSCu0wc "sed 4.2.2 – Try It Online")

### Sed (with `-r` switch), <s>53</s> 52 characters

 s/./&zyxwvutsrqponmlkjihgfedcba \n/g
 s/(.).*1円/1円/gm

In case trailing spaces are acceptable.

[Try it online!](https://tio.run/##DcJJDoAgDADAu6/gZNREGv/DRQVxAYrU/fFWJ0NGMxNIyJ/7Oo99o7RGDN4t8zTawei@a4UKYDOCQpayUg38rWcejXMoTkxOvxi3CQNxnT4 "sed 4.2.2 – Try It Online")

If this is an answer to a challenge…

…Be sure to follow the challenge specification. However, please refrain from exploiting obvious loopholes. Answers abusing any of the standard loopholes are considered invalid. If you think a specification is unclear or underspecified, comment on the question instead.
…Try to optimize your score. For instance, answers to code-golf challenges should attempt to be as short as possible. You can always include a readable version of the code in addition to the competitive one. Explanations of your answer make it more interesting to read and are very much encouraged.
…Include a short header which indicates the language(s) of your code and its score, as defined by the challenge.

More generally…

…Please make sure to answer the question and provide sufficient detail.
…Avoid asking for help, clarification or responding to other answers (use comments instead).

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Edit Summary*

Cancel

\$\begingroup\$ The capturing group in the first substitution can be removed, and the second substitution can be shortened by a bit. Additionally you can find another way to treat spaces (note the rules allow printing a space instead of a blank line when the char is a space) to golf it some more. \$\endgroup\$

user41805
– user41805

2019年11月21日 18:10:55 +00:00
Commented Nov 21, 2019 at 18:10
\$\begingroup\$ Thank you, @KritixiLithos. I was so happy I got rid of initial 77 character version with looping, that I forgot to recheck some details. \$\endgroup\$

manatwork
– manatwork

2019年11月21日 18:47:29 +00:00
Commented Nov 21, 2019 at 18:47
\$\begingroup\$ One more byte can be removed from the second substitution (60b), and you can use the approach by the 53-byte solution to get a valid solution shorter than the now 60 byte solution. \$\endgroup\$

user41805
– user41805

2019年11月22日 06:55:47 +00:00
Commented Nov 22, 2019 at 6:55
\$\begingroup\$ Thank you, @KritixiLithos. No I idea why I kept anchoring that expression. \$\endgroup\$

manatwork
– manatwork

2019年11月22日 18:37:40 +00:00
Commented Nov 22, 2019 at 18:37
\$\begingroup\$ Maybe you missed the second part of my comment, you can have s/ // at the end of the 52b solution to get a valid 58b solution \$\endgroup\$

user41805
– user41805

2019年11月23日 16:09:40 +00:00
Commented Nov 23, 2019 at 16:09

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