During the qualification round, the following question was asked:

You've been given a list of words to study and memorize. Being a diligent  
student of language and the arts, you've decided to not study them at all
and instead make up pointless games based on them. One game you've come up with
is to see how you can concatenate the words to generate the lexicographically
lowest possible string.

Input

As input for playing this game you will receive a text file containing 
an integer N, the number of word sets you need to play your game against. This
will be followed by N word sets, each starting with an integer M, the 
number of words in the set, followed by M words. All tokens in the input will 
be separated by some whitespace and, aside from N and M, will consist entirely 
of lowercase letters.

Output

Your submission should contain the lexicographically shortest strings for 
each corresponding word set, one per line and in order.

Constraints

1 <= N <= 100
1 <= M <= 9
1 <= all word lengths <= 10

Example input

5
6 facebook hacker cup for studious students
5 k duz q rc lvraw
5 mybea zdr yubx xe dyroiy
5 jibw ji jp bw jibw
5 uiuy hopji li j dcyi

Example output

cupfacebookforhackerstudentsstudious
duzklvrawqrc
dyroiymybeaxeyubxzdr
bwjibwjibwjijp
dcyihopjijliuiuy

The program I wrote goes as:

chomp($numberElements=<STDIN>);  

for(my $i=0; $i < $numberElements; $i++)  
{  
   my $string;  
   chomp ($string = <STDIN>);  
   my @array=split(/\s+/,$string);  
   my $number=shift @array;  
   @sorted=sort @array;    
   $sortedStr=join("",@sorted);    
   push(@data,$sortedStr);  
}  

foreach (@data)  
{  
  print "$_\n";  
}  

The program gives the correct output for the given test cases but still facebook shows it to be incorrect. Is there something wrong with the program??