Rating:
Programming 400 - Fibonacci
Script:
```perl
#!/usr/bin/perl -w
use IO::Socket;
use bigint;
my $data = '';
my $nc = IO::Socket::INET->new(
PeerAddr=>"54.175.35.248",
PeerPort=>8000,
Timeout=>10,
Type=>SOCK_STREAM) or die $@;
$nc->autoflush(1);
if ($nc) {
while (1) {
my $recv = sysread($nc, $data, 768);
print "\n$data";
# start
if ($data =~ /inform the number (.+?):/) {
kirim($1);
}
# capture questions and send answer
if ($data =~ /Stage (.+) -> N = (.+)/) {
my $jawab = recursive($2);
print ($jawab);
kirim($jawab);
}
# error handling
if ($recv == 0) {
print "*** Bye!\n";
exit(1);
}
if ($data =~ /Wrong/) {
print "*** Salah!\n";
exit(1);
}
}
}
# calculate recursive calls
sub recursive {
my $n = $_[0] + 1; #oupss
# fibonacci sequence
my ($a, $b) = (0, 1);
for (2..$n) {
($a, $b) = ($b, $a+$b);
}
# recursive calls formula
my $calls = (2 * $b - 2);
# get last 3 numbers
$calls = $calls % 1000;
return $calls;
}
sub kirim {
my $msg = $_[0];
print $nc "$msg\n";
}
```
Run:
```
$ perl solved_fibonacci.pl
```
Results:
```
..... cut .....
[+] Stage 97 -> N = 357
The answer is: 556
[+] Correct!
[+] Stage 98 -> N = 489
The answer is: 388
[+] Correct!
[+] Stage 99 -> N = 268
The answer is: 136
[+] Correct!
[+] Stage 100 -> N = 312
The answer is: 64
[+] Correct!
[+] Congratulations, the flag is: 3DS{g00d4lgorithmsC4nSaveYourTime}
*** Bye!
```
