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Challenges Build a replacement ball in regex.

Perl, 114 bytes Takes string and number as space-delimited line on stdin. Prints the regex to stdout. perl -aE'($_,$n)=@F;@s=/./g;$,="|";say grep{$n==y/1//&&s/./$&?".":$s[pos]/eg}map{...

posted 6mo ago by jhnc‭ · edited 6mo ago by jhnc‭

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#3: Post edited by

jhnc‭ · 2026-03-18T10:06:24Z (6 months ago)
preprocessing string into an array simplifies access

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~~# Perl, 115 bytes~~
Takes string and number as space-delimited line on stdin. Prints the regex to stdout.
```
~~perl -aE'($_,$n)=@F;$x=@s=/./g;$,="|";say grep{$n==y/1//&&s/./$&?".":$s[pos]/eg}map{sprintf"%0*b",$x,$_}1..2**$x-1'~~
```
Comments:
```
perl -aE'
# 1. load/preprocess string and n
($_,$n) = @F;
$x = @s = /./g;
# 2. set ouput field separator
$, = "|";
# 7. print resulting list of strings
say
grep {
# 5. ensure mask has correct number of bits set
# else discard
$n==y/1// &&
# 6. apply mask
s/./
$& # if mask is nonzero
? "." # then apply
: $s[pos] # else use original character
# (pos is offset of this match)
/eg
}
# 4. convert to bitmask
~~map { sprintf "%0*b",$x,$_ }~~
# 3. generate all integers from 1 to 2^(length of string)-1
~~1..2**$x-1~~
'
```
Am just learning about powersets so I expect this can be greatly improved.
~~[Try it online!][TIO-mmvulx0e]~~
[TIO-mmvulx0e]: https://tio.run/##RY7BagIxFEX38xUhRG2HzHuOpZuGWFf@hBWJQxRBJ0NeBMXop3eaVNTN5ebdwyGd9fvP/kiWbawJR2/ZiMx5pIrO79qwYXxAP@2A9JRxycRKMsJqCiWiZ/rGzogMG68KMV@Ml/pGKAWi6t8SKdp3PZsrcdIz0gi4VUJqHrlK/mLrbXcRrdZnrBGHQ0qAGH5z4F@CFp2jJdrt9WC6C90/wgfjcs2lOEmxutYAk7IUp6rus41z1TvJalZNGRQmPGqIBoqDc@3jkGo8QA4HOdydnvyPUKyNfz58BANxna7B0ouhEMFCDoIYILUAudkENobsC7RZkCPNDaTWZLAxT@PHHcyyvCTtvxGKX9eFnWupr8z@Dw "Perl 5 – Try It Online"

# Perl, 114 bytes
Takes string and number as space-delimited line on stdin. Prints the regex to stdout.
```
perl -aE'($_,$n)=@F;@s=/./g;$,="|";say grep{$n==y/1//&&s/./$&?".":$s[pos]/eg}map{sprintf"%0*b",@s+0,$_}1..2**@s-1'
```
Comments:
```
perl -aE'
# 1. load/preprocess string and n
($_,$n) = @F;
@s = /./g;
# 2. set ouput field separator
$, = "|";
# 7. print resulting list of strings
say
grep {
# 5. ensure mask has correct number of bits set
# else discard
$n==y/1// &&
# 6. apply mask
s/./
$& # if mask is nonzero
? "." # then apply
: $s[pos] # else use original character
# (pos is offset of this match)
/eg
}
# 4. convert to bitmask
map { sprintf "%0*b",@s+0,$_ }
# 3. generate all integers from 1 to 2^(length of string)-1
1..2**@s-1
'
```
Am just learning about powersets so I expect this can be greatly improved.
[Try it online!][TIO-mmvvig5t]
[TIO-mmvvig5t]: https://tio.run/##RY7BbsIwEETv/oqVa6BNwy6h6qWRaU78BK2QiQxFgjjymgMi8OlNbRD0MhrPjt9ua/3uvT@whbU14eAtjNgcR6Vo/bYJa5AD/moGrGcgc1DLHJjGM8yIPOgLHImAal8KNV9MvvWFKVdEZf8cm6p50dW8rFgT0qZUuZadLCNcCHY@wBOsnYdgOcCP8Y1lFmLjbXtSjdZHKoiGQ45f1fBTovxQvGgdf5PdnPemPfHtPjmYZCuZV/w6ydXyXCBOs6zicdGnTVKWvcuhgPEMUJhwt6EzKPbONfcg2m6PSRwmcbf29DpEsTL@8fAdGuxWMU2nP2IOHVpMwtgFjC5gcjYWa8P2v2gTIEkc1xhdnYq1eRDfbsUES5OIvRJR/Lo2bF3D/djs/gA "Perl 5 – Try It Online"

#2: Post edited by

jhnc‭ · 2026-03-18T09:43:10Z (6 months ago)
preprocessing string into an array simplifies access

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~~# Perl, 123 bytes~~
~~Takes string and number n on stdin. Prints the regex to stdout.~~
```
~~perl -aE'($s,$n)=@F;$x=length$s;$,="|";say~~
~~grep{$n==y/1//&&s/./$&?".":substr$s,pos,1/eg}map{sprintf"%0*b",$x,$_}1..2**$x-1'~~
```
Comments:
```
perl -aE'
~~# 1. load string and n~~
~~($s,$n) = @F;~~
~~$x = length $s;~~
# 2. set ouput field separator
$, = "|";
# 7. print resulting list of strings
say
grep {
# 5. ensure mask has correct number of bits set
# else discard
$n==y/1// &&
# 6. apply mask
s/./
~~$& # if mask is nonzero~~
~~? "." # then apply~~
~~: substr $s,pos,1 # else use original character~~
~~# (pos is offset of this match)~~
/eg
}
# 4. convert to bitmask
map { sprintf "%0*b",$x,$_ }
# 3. generate all integers from 1 to 2^(length of string)-1
1..2**$x-1
'
```
~~Am just learning about powersets. I expect this can be greatly improved.~~
~~[Try it online!][TIO-mmv93tw4]~~
[TIO-mmv93tw4]: https://tio.run/##RY5BbsIwEEX3OYVlGSiRM0Oouqll2hWXaCvkRCZFgjjyGAlE4OhNbRCw@fqeeXrjzvrt27Any9bWhL23bELmOFFZ5zdtWDM@ou92RHrBuGRiJRlhsYAc0TN9YUdEhrVXmVh@zX70hVAKRDW8CJKinerPpRIHvbVtE34FKSE177mKB7LG2@4kWq2PWCKOx4SAYvzBOPB32lcUfHJ0jmQ5Rducd6Y70e1PfDTLKy7FQYrVuQSY57k4FOWQvJyrwUlWsmLBIDPhXkNvINs5194HsfY7SOEghbvR8@sSssr4x8P3YKCv4jRYejIUerCQgqAPEFuA1GwEa0P2CdokSBHXNcRWJ7A2D@PrDUyytInaqxGyP9eFjWtpKMz2Hw "Perl 5 – Try It Online"

# Perl, 115 bytes
Takes string and number as space-delimited line on stdin. Prints the regex to stdout.
```
perl -aE'($_,$n)=@F;$x=@s=/./g;$,="|";say grep{$n==y/1//&&s/./$&?".":$s[pos]/eg}map{sprintf"%0*b",$x,$_}1..2**$x-1'
```
Comments:
```
perl -aE'
# 1. load/preprocess string and n
($_,$n) = @F;
$x = @s = /./g;
# 2. set ouput field separator
$, = "|";
# 7. print resulting list of strings
say
grep {
# 5. ensure mask has correct number of bits set
# else discard
$n==y/1// &&
# 6. apply mask
s/./
$& # if mask is nonzero
? "." # then apply
: $s[pos] # else use original character
# (pos is offset of this match)
/eg
}
# 4. convert to bitmask
map { sprintf "%0*b",$x,$_ }
# 3. generate all integers from 1 to 2^(length of string)-1
1..2**$x-1
'
```
Am just learning about powersets so I expect this can be greatly improved.
[Try it online!][TIO-mmvulx0e]
[TIO-mmvulx0e]: https://tio.run/##RY7BagIxFEX38xUhRG2HzHuOpZuGWFf@hBWJQxRBJ0NeBMXop3eaVNTN5ebdwyGd9fvP/kiWbawJR2/ZiMx5pIrO79qwYXxAP@2A9JRxycRKMsJqCiWiZ/rGzogMG68KMV@Ml/pGKAWi6t8SKdp3PZsrcdIz0gi4VUJqHrlK/mLrbXcRrdZnrBGHQ0qAGH5z4F@CFp2jJdrt9WC6C90/wgfjcs2lOEmxutYAk7IUp6rus41z1TvJalZNGRQmPGqIBoqDc@3jkGo8QA4HOdydnvyPUKyNfz58BANxna7B0ouhEMFCDoIYILUAudkENobsC7RZkCPNDaTWZLAxT@PHHcyyvCTtvxGKX9eFnWupr8z@Dw "Perl 5 – Try It Online"

#1: Initial revision by

jhnc‭ · 2026-03-18T00:15:33Z (6 months ago)

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# Perl, 123 bytes

Takes string and number n on stdin. Prints the regex to stdout.

```
perl -aE'($s,$n)=@F;$x=length$s;$,="|";say
grep{$n==y/1//&&s/./$&?".":substr$s,pos,1/eg}map{sprintf"%0*b",$x,$_}1..2**$x-1'
```

Comments:
```
perl -aE'
    # 1. load string and n
    ($s,$n) = @F;

    $x = length $s;

    # 2. set ouput field separator
    $, = "|";

    # 7. print resulting list of strings
    say
        grep {
            # 5. ensure mask has correct number of bits set
            #    else discard
            $n==y/1// &&

            # 6. apply mask
            s/./
                $&                 # if mask is nonzero
                ? "."              # then apply
                : substr $s,pos,1  # else use original character
                                   # (pos is offset of this match)
            /eg
        }

        # 4. convert to bitmask
        map { sprintf "%0*b",$x,$_ }

        # 3. generate all integers from 1 to 2^(length of string)-1
        1..2**$x-1
'
```

Am just learning about powersets. I expect this can be greatly improved.


[Try it online!][TIO-mmv93tw4]

[TIO-mmv93tw4]: https://tio.run/##RY5BbsIwEEX3OYVlGSiRM0Oouqll2hWXaCvkRCZFgjjyGAlE4OhNbRCw@fqeeXrjzvrt27Any9bWhL23bELmOFFZ5zdtWDM@ou92RHrBuGRiJRlhsYAc0TN9YUdEhrVXmVh@zX70hVAKRDW8CJKinerPpRIHvbVtE34FKSE177mKB7LG2@4kWq2PWCKOx4SAYvzBOPB32lcUfHJ0jmQ5Rducd6Y70e1PfDTLKy7FQYrVuQSY57k4FOWQvJyrwUlWsmLBIDPhXkNvINs5194HsfY7SOEghbvR8@sSssr4x8P3YKCv4jRYejIUerCQgqAPEFuA1GwEa0P2CdokSBHXNcRWJ7A2D@PrDUyytInaqxGyP9eFjWtpKMz2Hw "Perl 5 – Try It Online"

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