Perl Weekly Challenge 315.
My solutions (task 1 and task 2 ) to the The Weekly Challenge - 315.
Task 1: Find Words
Submitted by: Mohammad Sajid Anwar
You are given a list of words and a character.
Write a script to return the index of word in the list where you find the given character.
Example 1
Input: @list = ("the", "weekly", "challenge")
$char = "e"
Output: (0, 1, 2)
Example 2
Input: @list = ("perl", "raku", "python")
$char = "p"
Output: (0, 2)
Example 3
Input: @list = ("abc", "def", "bbb", "bcd")
$char = "b"
Output: (0, 2, 3)
I solve this straightforwardly using a Schwartzian transform of the words in the list, filtering the resulting list by the presence of the character and printing the surviving indices. The code fits a 1.5-liner.
Example 1:
perl -E '
($c,@x)=@ARGV;say "char: $c, words: @x -> ", join ",", map {$_->[0]} grep {$_->[1]=~/$c/}
map{[$_, $x[$_]]}0..@x-1
' e the weekly challenge
Results:
char: e, words: the weekly challenge -> 0,1,2
perl -E '
($c,@x)=@ARGV;say "char: $c, words: @x -> ", join ",", map {$_->[0]} grep {$_->[1]=~/$c/}
map{[$_, $x[$_]]}0..@x-1
' p perl raku python
Results:
char: p, words: perl raku python -> 0,2
perl -E '
($c,@x)=@ARGV;say "char: $c, words: @x -> ", join ",", map {$_->[0]} grep {$_->[1]=~/$c/}
map{[$_, $x[$_]]}0..@x-1
' b abc def bbb bcd
Results:
char: b, words: abc def bbb bcd -> 0,2,3
The full code is similar:
1 # Perl weekly challenge 315
2 # Task 1: Find Words
3 #
4 # See https://wlmb.github.io/2025/03/31/PWC315/#task-1-find-words
5 use v5.36;
6 die <<~"FIN" unless @ARGV>=2;
7 Usage: $0 C W0 W1...
8 to find the indices of the words Wn that contain the character C
9 FIN
10 my $char = shift;
11 die "Expected a single char" unless $char=~/^\w$/;
12 say "char: $char, words: @ARGV -> ",
13 join ",",
14 map {$_->[0]} # Extract indices
15 grep {$_->[1]=~/$char/} # Test word
16 map{[$_, $ARGV[$_]]} # Schwartzian transform
17 0..@ARGV-1;
Example:
./ch-1.pl e the weekly challenge
./ch-1.pl p perl raku python
./ch-1.pl b abc def bbb bcd
Results:
char: e, words: the weekly challenge -> 0,1,2
char: p, words: perl raku python -> 0,2
char: b, words: abc def bbb bcd -> 0,2,3
Task 2: Find Third
Submitted by: Mohammad Sajid Anwar
You are given a sentence and two words.
Write a script to return all words in the given sentence that appear
in sequence to the given two words.
Example 1
Input: $sentence = "Perl is a my favourite language but Python is my favourite too."
$first = "my"
$second = "favourite"
Output: ("language", "too")
Example 2
Input: $sentence = "Barbie is a beautiful doll also also a beautiful princess."
$first = "a"
$second = "beautiful"
Output: ("doll", "princess")
Example 3
Input: $sentence = "we will we will rock you rock you.",
$first = "we"
$second = "will"
Output: ("we", "rock")
I could solve the problem by building a regular expression to repeatedly fetch the word that follows the first two given words. This fits a long one-liner.
Example 1 (wrong, see below):
perl -E '
($f,$s,$r)=@ARGV;$e="$f\\W+$s\\W+(\\w+)";@o=$r=~/$e/g;say "first: $f, second: $s, \nsentence: $r\n-> @o"
' my favourite "Perl is my favourite language but Python is my favourite too."
Results:
first: my, second: favourite,
sentence: Perl is my favourite language but Python is my favourite too.
-> language too
Example 2:
perl -E '
($f,$s,$r)=@ARGV;$e="$f\\W+$s\\W+(\\w+)";@o=$r=~/$e/g;say "first: $f, second: $s, \nsentence: $r\n-> @o"
' a beautiful "Barbie is a beautiful doll also also a beautiful princess."
Results:
first: a, second: beautiful,
sentence: Barbie is a beautiful doll also also a beautiful princess.
-> doll princess
Example 3:
perl -E '
($f,$s,$r)=@ARGV;$e="$f\\W+$s\\W+(\\w+)";@o=$r=~/$e/g;say "first: $f, second: $s, \nsentence: $r\n-> @o"
' we will "we will we will rock you rock you"
Results:
first: we, second: will,
sentence: we will we will rock rock you rock you
-> we
Note that example 3 failed, as the second we is eaten away by the first match. In general, the /g modifier starts a repeated search where the previous one ended. We can avoid eating all the previously matched string by using a lookahead assertion. In the following code we just eat the first word, but keep from the second word onwards by adding a lookahead assertion into our regular expression.
Example 3’:
perl -E '
($f,$s,$r)=@ARGV;$e="$f\\W+(*pla:$s\\W+(\\w+))";@o=$r=~/$e/g;
say "first: $f, second: $s, \nsentence: $r\n-> @o"
' we will "we will we will rock you rock you"
Results:
first: we, second: will,
sentence: we will we will rock you rock you
-> we rock
This fixes example 3. We still have to verify examples 1 and 2 continue working:
Examples 1’ and 2’
perl -E '
($f,$s,$r)=@ARGV;$e="$f\\W+(*pla:$s\\W+(\\w+))";@o=$r=~/$e/g;
say "first: $f, second: $s, \nsentence: $r\n-> @o"
' my favourite "Perl is my favourite language but Python is my favourite too."
perl -E '
($f,$s,$r)=@ARGV;$e="$f\\W+(*pla:$s\\W+(\\w+))";@o=$r=~/$e/g;
say "first: $f, second: $s, \nsentence: $r\n-> @o"
' a beautiful "Barbie is a beautiful doll also also a beautiful princess."
Results:
first: my, second: favourite,
sentence: Perl is my favourite language but Python is my favourite too.
-> language too
first: a, second: beautiful,
sentence: Barbie is a beautiful doll also also a beautiful princess.
-> doll princess
The full code is:
1 # Perl weekly challenge 315
2 # Task 2: Find Third
3 #
4 # See https://wlmb.github.io/2025/03/31/PWC315/#task-2-find-third
5 use v5.36;
6 die <<~"FIN" unless @ARGV==3;
7 Usage: W1 W2 S
8 to find which words in sentence S follows words W1 and W2.
9 FIN
10 my ($first, $second, $sentence)=@ARGV;
11 for($first, $second){die "Expected a single word: $_" unless /^\w+$/}
12 my $re="$first\\W+(*pla:$second\\W+(\\w+))";
13 my @output=$sentence=~/$re/g;
14 say "first: $first, second: $second, \nsentence: $sentence\n-> @output"
Example:
./ch-2.pl my favourite "Perl is my favourite language but Python is my favourite too."
./ch-2.pl a beautiful "Barbie is a beautiful doll also also a beautiful princess."
./ch-2.pl we will "we will we will rock you rock you"
Results:
first: my, second: favourite,
sentence: Perl is my favourite language but Python is my favourite too.
-> language too
first: a, second: beautiful,
sentence: Barbie is a beautiful doll also also a beautiful princess.
-> doll princess
first: we, second: will,
sentence: we will we will rock you rock you
-> we rock
/;
Written on March 31, 2025