【PythonChallenge】Level 3

题目为正则表达式，需要注意EXACTLY的含义，即AAAAxBBB中x不满足条件，但aAAAxBBBa却满足条件。使用perl解决此题，利用s///替换字母，循环读取整个源码文件，结果为linkedlist。解答完毕，Perl程序如下：

#!perl -w
use 5.010;

############## Level 3 ##############

# data store the sourcepage information

open FILEIN, "data"
    or die "Can't open the data.";
    
my $word = "";    

while (<FILEIN>) {
    chomp;

    while ( $_ =~ s/(?<name1>[a-z])([A-Z]){3}(?<name2>[a-z])([A-Z]){3}(?<name3>[a-z])/$+{name2}AAA$+{name3}/ ) {
        $word .= $+{name2};
    }
}

close FILEIN;

print $word . "\n";

#################################