# File:	match2.pl
# Title:  From the assembling DNA problem
# You have 2 strings check if the suffix of s1 == prefix of s2
# In our problem we put s = s1.XX.s2 put XX in the middle as a FENCE
# XX is introduced by the programmer. Symbol X should not be to be found in s
# then look just at one string s
# Reminder $s =~ /(.{$n})/; # put in $1 first n chars 
# .{$n} - that is repeat .(anything) n times
#  () means set result in variable $1
#  \S = means non-whitespace char 
#  (.{2}) means put in $1 - 2 chars
#  (.{2,}) put in $1 more than 2 chars 
#   \1 matches text previously matched first
#   ([\S]{2,})XX\1/  - means 
# finds first XX, takes longest substring before XX and matches with substring after XX 
# Find suffix before XX and that matches prefix after XX
# Author:	Mihaela  Malita
$s = "ttaaaXXaaaammmmm";	 # find suffix aaa equal with prefix aaa in second string	
$s =~ /(.{2})XX/; # find substring before XX length 2 (find 2 chars before XX)
print $1, "\n"; # prints aa 
$s =~ /(.{2,})XX/; # find substring before XX longer than 2
print $1, "\n"; # prints ttaaa -maxim length {2,} means > 2
$s =~ /(.{3})XX\1/;  # look for 3 chars before XX, match is put in \1
print $1, "\n"; # prints aaa
print("Finds in  $s longest suffix before XX = with prefix after XX:\n");
$s =~ /([\S]{2,})XX\1/;  #  \1 takes the value of the first match - suffix  
print $1, "\n"; # prints aaa
exit;