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APL (Dyalog Unicode), 23 bytes Anonymous tacit prefix function. Reuires 0-based indexing (⎕IO←0) (⊢⍪⍨¯1↓⊢,∘↑-∘⍳∘≢↑¨⊢)⊢,⌽ Try it online! ⌽ reverse the argument ⊢, prepend the argument (…) ...

posted 4y ago by Adám‭

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#1: Initial revision by

Adám‭ · 2021-03-02T00:05:41Z (almost 4 years ago)

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# [APL (Dyalog Unicode)], 23 bytes

<!-- language-all: lang-apl -->

Anonymous tacit prefix function. Reuires 0-based indexing (`⎕IO←0`)

    (⊢⍪⍨¯1↓⊢,∘↑-∘⍳∘≢↑¨⊢)⊢,⌽

[Try it online!][TIO-klr8th27]

`⌽` reverse the argument

`⊢,` prepend the argument

`(`…`)` apply the following tacit function to that:

&emsp;`⊢` on the characters of the argument

&emsp;…`↑¨` of each character, take this many characters:

&emsp; `-∘⍳∘≢` the negative indices \$0…\text{length}-1\$

&emsp;…`∘↑` mix list of strings into character matrix, then:

&emsp; `⊢,` prepend the argument (vertically)

&emsp;`¯1↓` drop the last row

&emsp;`⊢⍪⍨` append the argument below


[APL (Dyalog Unicode)]: https://www.dyalog.com/
[TIO-klr8th27]: https://tio.run/##SyzI0U2pTMzJT///qG@qp/@jtgkG/zUedS161LvqUe@KQ@sNH7VNBnJ1HnXMeNQ2URdE9W4GkZ2LgPxDK4BymmD5nr3/04C6H/X2PepqftS75lHvlkPrjYFqgOYGBzkDyRAPz@D/aQrqHqk5OfnqAA "APL (Dyalog Unicode) – Try It Online"

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