Recursively remove adjacent duplicate characters - perl

Question

I am having a string say
$str = "hhiiishs aappllee eerrffdd"
I want to remove adjacent duplicate characters recursively from a string. I dont know how to write recursion. I have written a code that is not recursive but working if we pass string by string
use strict;
use warnings;
my $str = "AABBCCDEEFDDS asdwdwws ffoorr";
sub remove {
my $var1 = "";
my $str = $_[0];
my #arr = split (//, $str);
my $f = "";
foreach (0..$#arr) {
if ( $arr[$_] eq $var1) {
next;
#substr ( $str, $_)
} else {
$var1 = $arr[$_];
$f = "$f"."$arr[$_]";
}
}
$f = "$f"." ";
return $f;
}
Please guide me how to write recursive in Perl.

Answer 1

You can try,
$str =~ s/(.)\1+/$1/g;
gives
hishs aple erfd

Answer 2

Using recursion probably isn't the best choice for this, but here is a recursive function below.
#!/usr/bin/perl
use strict;
use warnings;
my $foo = "aabbccddeeffgg hhiijjkkllmmnnoo pp";
print reDup($foo), "\n";
sub reDup {
my #string = split ('', shift); #split string into array of characters
my $val;
for my $i( 0..$#string){
if(defined($val) && $string[$i] eq $val){
#string[$i..$#string] = #string[($i+1)..$#string]; #if last char checked = current char, shift the array to the left.
pop #string; #Above leaves unwanted element at the end, so pop it off
my $str = join('', #string);
return reDup($str); #do it all again
}
$val = $string[$i];
}
return join('', #string); #when the for loops if statement is never executed, it must contain no duplicates.
}

Answer 3

sub _remove_adjacent {
my $out = shift;
if (#_ == 0) {
return $out;
}
elsif (#_ == 1) {
return $out.$_[0];
}
elsif ($_[0] eq $_[1]) {
shift;
return _remove_adjacent($out.shift(#_), #_);
} else {
return _remove_adjacent($out.shift(#_), #_);
}
}
sub remove_adjacent {
my ($in) = #_;
return _remove_adjacent('', split(//, $in));
}
Of course, that's purely tail-recursive, so it can be inlined into a loop.
sub remove_adjacent {
my ($in) = #_;
my #in = split(//, $in);
my $out = '';
while (1) {
if (#in == 0) {
last;
}
elsif (#in == 1) {
$out .= $in[0];
last;
}
elsif ($in[0] eq $in[1]) {
shift(#in);
$out .= shift(#in);
} else {
$out .= shift(#in);
}
}
return $out;
}
This can be cleaned up further, but it shows that recursion would be a pure waste here.