Solution to task 2

1 files changed, 107 insertions, 0 deletions

diff --git a/challenge-099/jo-37/perl/ch-2.pl b/challenge-099/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use experimental 'signatures';
+use charnames ':full';
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV == 2;
+usage: $0 [-examples] [-tests] [-verbose] [string sequence]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-verbose
+    show subsequence in string
+
+string
+    string to examine
+
+sequence
+    sequence of chars to search for in <string>
+
+EOS
+
+
+### Input and Output
+
+say matchseq($ARGV[0], $ARGV[1]);
+
+
+### Implementation
+
+# Count occurences of a character sequence within a string.
+sub matchseq ($str, $seq) {
+
+    # Create a regex that matches the character sequence and captures
+    # all of its characters individually.
+    # Example transformation chain:
+    # 'x*' -> ('x', '*') -> ('x', '\\*') -> (?:(x).*?(\*))
+    my $seqmatch = sub {
+        local $" = ').*?(';
+        qr{(@_)};
+    }->(map quotemeta, split //, $seq);
+
+    # Find all sequence matches and collect the character match offsets.
+    my @match;
+    $str =~ m{ $seqmatch (?{push @match, [@-]}) (*FAIL) }x;
+
+    explainseq($str, $seq, $seqmatch, \@match) if $verbose;
+
+    # Return the number of matches.
+    scalar @match;
+}
+
+# Show the locations of the character sequence within the string.
+sub explainseq ($str, $seq, $re, $matches) {
+
+    say "sequence: '$seq'";
+    say "matcher:  $re";
+    say $str;
+
+    for my $match (@$matches) {
+
+        # Discard match offset, keeping submatches only. (See @-)
+        shift @$match;
+
+        # Prepare a string having the same length as $str.
+        my $seqloc = "\N{MIDDLE DOT}" x length $str;
+
+        # Overwrite the string at match offsets with chars from the
+        # sequence.
+        while (my ($idx, $offs) = each @$match) {
+            substr($seqloc, $offs, 1) = substr($seq, $idx, 1);
+        }
+        say $seqloc;
+    }
+}
+
+### Examples and tests
+
+sub run_tests {
+SKIP: {
+    skip "examples" unless $examples;
+    is matchseq('littleit', 'lit'), 5, 'example 1';
+    is matchseq('london', 'lon'), 3, 'example 2';
+}
+
+SKIP: {
+    skip "tests" unless $tests;
+    is matchseq('xxaxxbxxcxx', 'abc'), 1, 'unique sequence';
+    is matchseq('aaaaa', 'a'), 5, 'repetition';
+    is matchseq('ihgfedcba', 'def'), 0, 'not found';
+    is matchseq('a.b*c[d0e-f9g]h', '.*[0-9]'), 1, 'meta characters';
+        is matchseq('aa1', '.*[0-9]'), 0, 'not matching "regex"';
+        is matchseq('a.b.c', '.'), 2, 'matching literal dot'
+	}
+
+    done_testing;
+    exit;
+}