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Re: counting overlapping patterns

by Limbic~Region (Chancellor)
 on Feb 18, 2005 at 20:30 UTC ( #432504=note: print w/replies, xml ) Need Help??

in reply to counting overlapping patterns

Anonymous Monk,
Here is some code that covers your example, but it admittedly only works on fixed strings since it doesn't use regular expressions at all.
```#!/usr/bin/perl
use strict;
use warnings;

print str_count('AAAA', 'AA'), "\n";

sub str_count {
my (\$str, \$pat) = @_;
my \$tot;
for ( 0 .. length( \$str ) - length( \$pat ) ) {
\$tot++ if index(\$str, \$pat, \$_) - \$_ == 0;;
}
return \$tot;
}

Cheers - L~R

Replies are listed 'Best First'.
Re^2: counting overlapping patterns
by Limbic~Region (Chancellor) on Feb 19, 2005 at 16:14 UTC
While discussing other methods that avoided regular expressions in the CB with bobf and nothingmuch, I mentioned an unpack/hash solution. nothinmuch asked to see it, so here is a highly untested alternative.
```#!/usr/bin/perl
use strict;
use warnings;

print str_count('ABAABAAAA', 'AA'), "\n";

sub str_count {
my (\$str, \$pat) = @_;
my %substr;
my (\$p_len, \$s_len) = (length \$pat, length \$str);

my \$template = ("A\$p_len" . 'X' . (\$p_len - 1)) x (\$s_len - \$p_len
+ + 1);
\$substr{\$_}++ for unpack \$template, \$str;
return \$substr{\$pat};
}

Cheers - L~R

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