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#!/usr/bin/env perl
# -*- Mode: cperl; cperl-indent-level:4 tab-width: 8; indent-tabs-mode: nil -*-
# -*- coding: utf-8 -*-
use strict; use warnings;
use Getopt::Long qw(:config no_ignore_case);
use Pod::Usage;
BEGIN {
$::debugging = 0;
my $help = 0;
GetOptions( 'debug' => \$::debugging,
"help" => \$help
) or pod2usage(2);
pod2usage( -exitval => 0, -verbose => 2 ) if $help;
our $dprint = sub( @ ) {
++$|;
print STDERR "[DBG] ",@_;
};
*::dprint = $::debugging ? $dprint : sub {};
}
=pod
=head1 Character Swapping
ch-1.pl [--debug] [--help] "String to swap" [Count] [Offset]
=cut
sub charactersSwappedAsExplain ( $$$ ) {
=pod
=head1 Challenge
You are given a string $S of size $N.
=cut
my ( $S, $C, $O ) = @_;
my $N = length $S;
=pod
You are also given swap count $C and offset $O such that
$C >= 1, $O >= 1 and $C + $O <= $N.
=cut
::dprint "in charactersSwappedAsExplain:\n";
die_if_invalid_value( $C, $O, $N );
=pod
Write a script to perform character swapping like below:
$S[ 1 % $N ] <=> $S[ (1 + $O) % $N ]
$S[ 2 % $N ] <=> $S[ (2 + $O) % $N ]
$S[ 3 % $N ] <=> $S[ (3 + $O) % $N ]
...
...
$S[ $C % $N ] <=> $S[ ($C + $O) % $N ]
=cut
for my $c ( 1 .. $C ) {
my $bak;
my $bak_r = '';
$bak_r = substr $S, ( $c + $O ) % $N, 1 if $::debugging;
$bak = substr $S, $c % $N, 1,
( defined $bak_r ? $bak_r : substr( $S, ( $c + $O ) % $N, 1 ) );
substr $S, ( $c + $O ) % $N, 1, $bak;
# or according to https://perldoc.perl.org/functions/substr.html
#substr( $S, ( $c + $O ) % $N, 1 ) = $bak;
::dprint "Character Swapping:\n";
::dprint "swap $c: $bak <=> $bak_r = $S\n";
}
=pod
Input:
$S = 'perlandraku'
$C = 3
$O = 4
Character Swapping:
swap 1: e <=> n = pnrlaedraku
swap 2: r <=> d = pndlaerraku
swap 3: l <=> r = pndraerlaku
Output:
pndraerlaku
=cut
return $S;
}
=pod
=head1 My Solution
I could simplyfy the process a little bit because I ccould divide the
pattern into 3 groups ( I wrote alphabet `O' as Ou for clearity of meaning. )
=over
=item 1. when C < O, each index numbers are devided into 5 groups
[ 0 ] [ C+2 .. C+Ou ] [ C+1 .. Ou ] [ 1 .. C ] [ C+Ou+1 .. N-1 ]
=item 2. C == 0
[ 0 ] [ C+2 .. C+Ou ] [ 1 .. C ] [ C+Ou+1 .. N-1 ]
=item 3. C > 0
[ 0 ] [ C+2 .. C+Ou ][ C-Ou .. C ] [ 1.. C+Ou+ 1 ] [ C+O+2 .. N-1 ]
=back
So I realized that part #1, #2 are always has the same rule, and follow things.
( note: K = boolean( C > Ou ) )
=over
=item Part #3
part #3 can rewritten as if K { [ (C-O) .. C ] } else { [ C+1 .. Ou ] }
=item Part #4
part #4 can be rewritten as [ 1 .. ( C + ( K *(Ou+1) ) ) ]
=item Part #5
part #5 can be rewritten as [ ( C+Ou+1+K ) .. N-1 ]
=back
=cut
sub charactersSwapped_DBG ( $$$ ) {
my ( $S, $C, $O ) = @_;
my $N = length $S;
my $K = int( $C > $O );
::dprint "in charactersSwapped_DBG:\n";
die_if_invalid_value( $C, $O, $N );
my $n;
my $part = substr $S, 0, 1; # P1
::dprint "P".++$n.": $part\n";
my $result = $part;
$part = substr $S, $C+2, ( $O-1 ); # P2
::dprint "P".++$n.": $part\n";
$result .= $part;
$part = ( $K ? substr( $S, $C-$O, $O+1 )
: substr( $S, $C+1, ( $O-$C ) ) ); # P3
::dprint "P".++$n.": $part\n";
$result .= $part;
$part = substr( $S, 1, $C + ( $K*($O+1) ) ); # P4
::dprint "P".++$n.": $part\n";
$result .= $part;
$part =substr( $S, ($C+$O+1+$K), ($N-$C-$O-$K-1) ); # P5
::dprint "P".++$n.": $part\n";
$result .= $part;
return $result;
}
sub charactersSwapped ( $$$ ) {
my ( $S, $C, $O ) = @_;
my $N = length $S;
my $K = int( $C > $O );
::dprint "in charactersSwapped:\n";
die_if_invalid_value( $C, $O, $N );
my $result = substr $S, 0, 1; # P1
$result .= substr $S, $C+2, ( $O-1 ); # P2
$result .= ( $K ? substr( $S, $C-$O, $O+1 )
: substr( $S, $C+1, ( $O-$C ) ) ); # P3
$result .= substr( $S, 1, $C + ( $K*($O+1) ) ); # P4
$result .=substr( $S, ($C+$O+1+$K), ($N-$C-$O-$K-1) ); # P5
return $result;
}
sub die_if_invalid_value( $$$ ) {
my ( $C, $O, $N ) = @_;
unless ( $C >=1 || $O >=1 ) {
die "[ERR] C(count) and O(Offset) must be equal or more than 1";
}
unless ( ( $C + $O ) <= $N ) {
die "[ERR] \$C($C) + \$O($O) <= \$N($N)";
}
}
package main;
my $Str = shift // 'perlandraku';
my $Cnt = shift // 3;
my $Off = shift // 4;
my $answer = '';
my $try;
if ( $::debugging ) {
$answer = charactersSwappedAsExplain( $Str, $Cnt, $Off );
$try = charactersSwapped_DBG( $Str, $Cnt, $Off );
}
else {
$try = charactersSwapped( $Str, $Cnt, $Off );
}
print STDERR "Output:\n";
::dprint "Expected Answer: ".$answer.$/;
::dprint "And.. my Answer: ";
print $try.$/;
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