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#!/usr/bin/env perl
use strict;
use warnings;
use feature qw{ say signatures state };
no warnings qw{ experimental::signatures };
use Carp;
use Getopt::Long;
# base case is the example;
my $string = 'perlandroku';
my $count = 3;
my $offset = 4;
GetOptions(
'string=s' => \$string,
'count=i' => \$count,
'offset=i' => \$offset,
);
# constraints
my $n = length $string;
$n >= 0 || croak 'String too short';
$count >= 1 || croak 'Swap Count < 1';
$offset >= 1 || croak 'Offset < 1';
$count <= $offset || croak 'Count > Offset';
$offset + $count < $n || croak 'Offset + Count < length of String';
char_swap( $string, $count, $offset );
sub char_swap ( $string, $count, $offset ) {
my $n = length $string;
print <<"END";
Input:
S: $string
C: $count
O: $offset
Character Swapping:
END
for my $c ( 1 .. $count ) {
# the locations within the string
my $p1 = ( $c % $n );
my $p2 = ( $c + $offset ) % $n;
# the characters in said positions
my $c1 = substr $string, $p1, 1;
my $c2 = substr $string, $p2, 1;
# since we have the characters stored already
# we don't need to store one and place the other
substr( $string, $p1, 1 ) = $c2;
substr( $string, $p2, 1 ) = $c1;
say qq{ swap $c: $c1 <=> $c2 = $string};
}
print <<"END";
Output:
$string
END
}
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