La tua sfida è espandere alcune parentesi nell'input di un programma come mostrato:

1. Trova una stringa s tra due parentesi corrispondenti [e ], con una singola cifra n dopo la parentesi chiusa.
2. Rimuovere le staffe.
3. Sostituisci s con se stesso ripetuto n volte. (Se n è 0, rimuovi semplicemente s .)
4. Andare al passaggio 1 fino a quando non ci sono più parentesi corrispondenti nell'input.

Ulteriori regole e chiarimenti:

• Prenderai input e fornirai output con qualsiasi mezzo consentito.
• È consentita una nuova riga finale nell'output.
• È sufficiente gestire ASCII stampabile nell'input.
• Si può presumere che tutte le parentesi corrispondano, ovvero non si riceverà mai l'input []]]]o [[[[].
• Si può presumere che ogni parentesi di chiusura ]abbia una cifra dopo di essa.

Casi test:

Input                -> Output
[Foo[Bar]3]2         -> FooBarBarBarFooBarBarBar
[one]1[two]2[three]3 -> onetwotwothreethreethree
[three[two[one]1]2]3 -> threetwoonetwoonethreetwoonetwoonethreetwoonetwoone
[!@#[$%^[&*(]2]2]2   -> !@#$%^&*(&*($%^&*(&*(!@#$%^&*(&*($%^&*(&*(
[[foo bar baz]1]1    -> foo bar baz
[only once]12        -> only once2
[only twice]23456789 -> only twiceonly twice3456789
[remove me!]0        -> 
before [in ]2after   -> before in in after

Poiché si tratta di code-golf , vince la risposta più breve in ogni lingua. In bocca al lupo!

Gema , 17 personaggi

[#]?=@repeat{?;#}

Esecuzione di esempio:

bash-4.4$ gema '[#]?=@repeat{?;#}' <<< '[three[two[one]1]2]3'
threetwoonetwoonethreetwoonetwoonethreetwoonetwoone

Retina , 24 23 22 byte

+`\[([^][]*)](.)
$2*$1

Provalo online! Questo è praticamente integrato in Retina 1. Modifica: salvato 1 byte grazie a @Kobi. 47 45 byte in Retina 0.8.2:

].
]$&$*¶
{+`\[([^][]*)]¶
$1[$1]
\[([^][]*)]

Provalo online!

Haskell , 101 96 byte

fst.(""%)
infix 4%
s%']':d:r=(['1'..d]>>s,r)
s%'[':r|(t,q)<-""%r=s++t%q
s%x:r=s++[x]%r
s%e=(s,e)

Provalo online! Invece di usare espressioni regolari come la maggior parte delle altre risposte, questo implementa un parser ricorsivo.

-5 byte grazie a BMO !

Perl 5 , 34 33 29 + 1 ( -p) = 30 byte

s/.([^[]*?)](.)/$1x$2/e&&redo

Provalo online!

Abbattilo con l'aiuto di @Shaggy e @TonHospel.

Japt v2 , 21 20 19 byte

Salvato 2 byte grazie a @Shaggy

e/.([^[]*?)](./@YpZ

Provalo online!

eè la sostituzione ricorsiva, che effettua una sostituzione alla volta fino a quando non ci sono più partite. In questo caso, le corrispondenze della regex /\[([^[]*?)](\d)/gvengono sostituite con <testo interno> ripetute volte <digit> fino a quando non ci sono più corrispondenze.

Secondo quanto ho pianificato ( qui ), questo regex dovrebbe essere più corto di almeno 3 2 byte:

‹[“⁽[»₋”]“.›

JavaScript, 71 67 66 byte

Ho avuto una soluzione 54 byte ma ha ottenuto fregati dal secondo banco di prova! :(

f=s=>s!=(x=s.replace(/.([^[]*?)](.)/,(_,y,z)=>y.repeat(z)))?f(x):x

Casi test

f=s=>s!=(x=s.replace(/.([^[]*?)](.)/,(_,y,z)=>y.repeat(z)))?f(x):x
o.innerText=`[Foo[Bar]3]2
[one]1[two]2[three]3
[three[two[one]1]2]3
[!@#[$%^[&*(]2]2]2
[[foo bar baz]1]1
[only once]12
[only twice]23456789
[remove me!]0
before [in ]2after`.split`\n`.map(x=>x.padEnd(22)+`:  `+f(x)).join`\n`

<pre id=o></pre>

Python 3 , 110 93 92 byte

import re
f=lambda s:f(re.sub(r'\[([^][]+)\](.)',lambda m:m[1]*int(m[2]),s))if'['in s else s

Provalo online!

-17 byte grazie a pizzapants184 -1 byte grazie a Kevin Cruijssen

Scala , 173 byte

l.foreach{x=>def r(c:String):String={val t="""\[([^\[\]]*)\](.)""".r.unanchored;c match{case t(g,h)=>r(c.replaceAllLiterally(s"[$g]$h",g*h.toInt));case _=>c}};println(r(x))}

Provalo online!

Allargato:

l.foreach { x =>
  def remove(current: String): String = {
    val test ="""\[([^\[\]]*)\](.)""".r.unanchored
    current match {
      case test(g, h) => remove(current.replaceAllLiterally(s"[$g]$h", g * h.toInt))
      case _ => current
    }
  }

  println(remove(x))
}

Vecchia soluzione

Scala , 219 215 213 212 199 byte

l.foreach{x=>def r(c:String):String={"""\[([^\[\]]*)\](.)""".r.findFirstMatchIn(c).map{x=>val g=x.group(1);val h=x.group(2).toInt;r(c.replaceAllLiterally(s"[$g]$h",g*h))}.getOrElse(c)};println(r(x))}

Provalo online!

Allargato:

l.foreach { x =>
  def remove(current: String): String = {
    """\[([^\[\]]*)\](.)""".r.findFirstMatchIn(current).map { x =>
      val g = x.group(1)
      val h = x.group(2).toInt
      remove(current.replaceAllLiterally(s"[$g]$h", g * h))
    }.getOrElse(current)
  }
  println(remove(x))
}

Dove sono la lista delle stringhe che elaboreremo.

Grazie Kevin Cruijssen per -1 byte

È passato da 212 a 199 rimuovendo un parametro inutilizzato, non ha prestato attenzione.

Impilato , 39 38 byte

Salvato 1 byte grazie a Shaggy, ha giocato a golf con regex!

['\[([^[\]]+)](.)'{.y x:x#~y*}recrepl]

Provalo online!

Sostituisce semplicemente in modo ricorsivo una regex '\[([^[\]]+)](.)'con la regola di ripetizione.

Python 3, 155 148 101 97 bytes

def f(x):
 a=x.rfind('[')
 if~a:b=x.find(']',a);x=f(x[:a]+x[a+1:b]*int(x[b+1])+x[b+2:])
 return x

Try It Online

Thanks to HyperNeutrino and Mego for -47 bytes and user202729 for -4 bytes.

JavaScript - 77 75 72 bytes

f=a=>a.replace(/(.*)\[([^[]*?)](.)(.*)/,(a,b,c,d,e)=>f(b+c.repeat(d)+e))

Edit: updated regex with Shaggy's recommendation

Snippet:

const test = ["[Foo[Bar]3]2", "[one]1[two]2[three]3", "[three[two[one]1]2]3", "[!@#[$%^[&*(]2]2]2", "[[foo bar baz]1]1", "[only once]12", "[only twice]23456789", "[remove me!]0", "before [in ]2after"];

const f=a=>a.replace(/(.*)\[([^[]*?)](.)(.*)/,(a,b,c,d,e)=>f(b+c.repeat(d)+e))

d.innerHTML=test.map(f).join("<br>");

<p id="d">

QuadR with the ≡ argument, 30 28 bytes

\[[^[]+?].
∊(⍎⊃⌽⍵M)⍴⊂1↓¯2↓⍵M

Try it online!

\[[^[]+?]. replace "[non-[ stuff]character" with

¯2↓⍵M drop the last two characters of the Match ("]digit")
1↓ drop the first character ("[")
⊂ enclose to be treated as a whole
(…)⍴ reshape to length:
 ⌽⍵M reverse the Match
 ⊃ pick the first (the digit)
 ⍎ evaluate
∊ ϵnlist (flatten)

≡ repeat until no more changes happen

The equivalent Dyalog APL function is 47 bytes:

'\[[^[]+?].'⎕R{∊(⍎⊃⌽⍵.Match)⍴⊂1↓¯2↓⍵.Match}⍣≡

Try it online!

Java 8, 250 249 241 239 bytes

s->{for(;s.contains("[");)for(int i=0,j,k;i<s.length();)if(s.charAt(i++)==93){String t="",r=t;for(j=k=s.charAt(i)-48;j-->0;)t+=s.replaceAll(r="(.*)\\[([^\\]]+)\\]"+k+"(.*)","$2");s=k<1?t:s.replaceFirst(r,"$1$3").replace("",t);}return s;}

-2 bytes thanks to @JonathanFrech (code contains two unprintable ASCII characters now, which can be seen in the TIO-link below).

Sigh... Java with regex is so damn limited.. I'll just quote myself from another answer here:

Replacing WWWW with 222W is easy in Java, but with 4W not.. If only Java had a way to use the regex capture-group for something.. Getting the length with "$1".length(), replacing the match itself with "$1".replace(...), converting the match to an integer with new Integer("$1"), or using something similar as Retina (i.e. s.replaceAll("(?=(.)\\1)(\\1)+","$#2$1")) or JavaScript (i.e. s.replaceAll("(.)\\1+",m->m.length()+m.charAt(0))) would be my number 1 thing I'd like to see in Java in the future to benefit codegolfing.. >.> I think this is the 10th+ time I hate Java can't do anything with the capture-group match..
Quote from here.

Explanation:

Try it online.

s->{                           // Method with String as both parameter and return-type
  for(;s.contains("[");)       //  Loop as long as the String contains a block-bracket
    for(int i=0,j,k;i<s.length();)
                               //   Inner loop over the characters of the String
      if(s.charAt(i++)==93){   //    If the current character is a closing block-bracket:
        String t="",r=t;       //     Create two temp-Strings, starting empty
        for(j=k=s.charAt(i)-48;//     Take the digit after the closing bracket
            j-->0;)            //     Loop that many times:
          t+=s.replaceAll(r="(.*)\\[([^\\]]+)\\]"+k+"(.*)","$2");
                               //      Append `t` with the word inside the block brackets
        s=k<1?                 //     If the digit was 0:
           t                   //      Replace the input with an empty String as well
          :                    //     Else:
           s.replaceFirst(r,"$1$3").replace("",t);}
                               //      Replace the word between brackets by `t`,
                               //      and remove the digit
  return s;}                   //  Return the modified input-String as result

Wolfram Language (Mathematica), 86 bytes

#//.s_:>StringReplace[s,"["~~x:Except["["|"]"]...~~"]"~~d_:>""<>x~Table~FromDigits@d]&

Try it online!

C, 407 368 bytes

Thanks to Jonathan Frech for saving bytes.

golfed (file bracket.c):

i,j,k,l,n;char*f(a,m)char*a;{for(i=0;a[i];++i){a[i]==91&&(j=i+1);if(a[i]==93){k=a[i+1]-48;if(!k){for(l=i+2;l<m;)a[++l-i+j-4]=a[l];a=realloc(a,m-3);return f(a,m-3);}for(l=j;l<i;)a[~-l++]=a[l];for(l=i+2;l<m;)a[++l-4]=a[l];m-=3;n=m+~-k*(i---j--);a=realloc(a,n);for(l=i;l<m;)a[l+++~-k*(i-j)]=a[l];for(m=0;m<k;++m)for(l=j;l<i;)a[l+++m*(i-j)]=a[l];return f(a,n);}}return a;}

ungolfed with program:

#include <stdlib.h>
#include <stdio.h>

// '[' = 133
// ']' = 135
// '0' = 48

i, j, k, l, n;

char* f(a,m) char*a;
{
  for (i=0; a[i]; ++i) {
    a[i]==91&&(j=i+1);

    if (a[i]==93) {
      k=a[i+1]-48;

      if (!k) {
        for (l=i+2; l<m; )
          a[++l-i+j-4] = a[l];

        a = realloc(a,m-3);
        return f(a,m-3);
      }
      for (l=j;l<i;)
        a[~-l++] = a[l];
      for (l=i+2; l<m; )
        a[++l-4] = a[l];
      m -= 3;
      n = m+~-k*(i---j--);
      a = realloc(a,n);

      for (l=i; l<m; )
        a[l+++~-k*(i-j)] = a[l];
      for (m=0; m<k; ++m)
        for (l=j; l<i;)
          a[l+++m*(i-j)] = a[l];

      return f(a,n);
    }
  }
  return a;
}

int main()
{
  char c[]="[Foo[Bar]3]2";
  char *b;

  char cc[]="[remove me!]0";
  char *bb;

  char ccc[]="[only once]12";
  char *bbb;

  b=malloc(13);
  bb=malloc(14);
  bbb=malloc(14);

  for (i=0; i<13; ++i)
    b[i] = c[i];

  for (i=0; i<14; ++i)
    bb[i] = cc[i];

  for (i=0; i<14; ++i)
    bbb[i]=ccc[i];

  printf("%s\n", f(b, 13));
  printf("%s\n", f(bb, 14));
  printf("%s\n", f(bbb, 14));

  return 0;
}

Compiled with gcc 5.4.1, gcc bracket.c

Red, 147 bytes

f: func[t][a: charset[not"[]"]while[parse t[any a some[remove["["copy h any a"]"copy d a](insert/dup v: copy""h to-integer d)insert v | skip]]][]t]

Ungolfed:

f: func [t][
    a: charset [not "[]"]                          ; all chars except [ and ]
    while [ parse t [                              ; repeat while parse is returning true
        any a                                      ; 0 or more chars other than [ and ]
        some [                                     ; one or more block:
            remove ["[" copy h any a "]" copy d a] ; remove the entire block, store the
                                                   ; substring between the [] in h,
                                                   ; the digit into d
            (insert/dup v: copy "" h to-integer d) ; makes d copies of h 
            insert v                               ; and inserts them in place 
            | skip ]                               ; skip if no match
        ]                                       
    ][]                                            ; empty block for 'while'
    t                                              ; return the modified string
]

I started learning Red's Parse dialect only yesterday, so I'm sure my code can be improved further. Parse is incomparably more verbose than regex, but is very clear, flexible and readable and can be freely mixed with the rest of the Red language.

Try it online!

Jelly, 30 bytes

œṡ”]µḢUœṡ”[ẋ€1¦Ṫ©Ḣ$FṚ;®
Çċ”]$¡

Try it online!

Explanation.

œṡ”]µḢUœṡ”[ẋ€1¦Ṫ©Ḣ$FṚ;®    Helper link 1, expand once.
                           Assume input = "ab[cd]2ef".

œṡ      Split at first occurence of
  ”]      character "]".
    µ   Start new monadic chain. Value = "ab[cd","2ef".

Ḣ       Ḣead. "ab[cd"
 U      Upend. "dc[ba"
  œṡ”[  Split at first occurence of "[". | "dc","ba".

ẋ€        Repeat ...
  1¦        the element at index 1...
          by ...
    Ṫ Ḣ$    the Ḣead of the Ṫail of ...
          the input list ("ab[cd","2ef") (that is, 2)

          The command Ḣ also pop the head '2'. The remaining
            part of the tail is "ef".
     ©    Meanwhile, store the tail ("ef") to the register.

          Current value: "dcdc","ba"
FṚ        Flatten and Ṛeverse. | "abcdcd"
  ;®      Concatenate with the value of the register. "abcdcdef"

Çċ”]$¡    Main link.

 ċ”]$     Count number of "]" in the input.
     ¡    Repeatedly apply...
Ç           the last link...
            that many times.

C,381 bytes

Compact version:

while(1){int t=strlen(i);int a,c=-1;char*w;char*s;char*f;while(c++<t){if(i[c]==']'){int k=c-a;w=calloc((k--),1);memcpy(w,&i[a+1],k);s=calloc((t-c-1),1);memcpy(s,&i[c+2],t-c-2);i[a]=0;int r=i[c+1]-48;if(r==0){f=calloc(t,1);sprintf(f,"%s%s",i,s);}else{f=calloc((t+k),1);sprintf(f,"%s%s[%s]%d%s",i,w,w,r-1,s);}free(i);i=f;break;}else if(i[c]=='[')a=c;}free(w);free(s);if(c>=t)break;}

Full version:

#include <string.h>
#include <stdio.h>
#include <stdlib.h>

void proceed(char* input)
{
  while(1)
  {
    int t=strlen(input);
    int start,cursor=-1;
    char* word;
    char* suffix;
    char* final;
    while(cursor++<t)
    {
      if(input[cursor]==']')
      {
        int wordlength = cursor-start;
        word=calloc((wordlength--),sizeof(char));
        memcpy(word, &input[start+1], wordlength );
        suffix=calloc((t-cursor-1),sizeof(char));
        memcpy( suffix, &input[cursor+2], t-cursor-2 );
        input[start]='\0';
        int rep=input[cursor+1]-'0';
        if(rep==0)
        {
          final=calloc(t,sizeof(char));
          sprintf(final,"%s%s",input,suffix);
        }
        else
        {
          final=calloc((t+wordlength+5),sizeof(char));
          sprintf(final,"%s%s[%s]%d%s",input,word,word,rep-1,suffix);
        }
        free(input);
        input=final;
        break;
      }
      else if(input[cursor]=='[')
        start=cursor;
    }
    free(word);
    free(suffix);

    if(cursor>=t)break;
  }
}

int main()
{
  char* input=calloc(256,sizeof(char));
  sprintf(input,"a[[toto]2b]2[ana]3");
  printf("in : %s\n",input);
  proceed(input);
  printf("out: %s\n",input);
  return 0;
}

Python, 80 bytes

import re
b=re.sub
s=lambda x:eval(b(r"\](.)",r"')*\1+'",b(r"\[","'+('","%r"%x)))

Try it online!

s("[Foo[Bar]3]2") Converts [Foo[Bar]3]2 to ''+('Foo'+('Bar')*3+'')*2+'', and evaluates.

Fails for input with quotes in brackets (e.g. [']3)