rlm@0: #!/usr/bin/perl
rlm@0: 
rlm@0: $a = "/home/r/coderloop-test/reversesequence-a.in";
rlm@0: $b = "/home/r/coderloop-test/reversesequence-b.in";
rlm@0: $c = "/home/r/coderloop-test/reversesequence-c.in";
rlm@0: 
rlm@0: %test_map = ("a" => "b", "b" => "c");
rlm@0: 
rlm@0: sub create_map{
rlm@0:   ## creates a "linked map" from a string representing
rlm@0:   ## the input file.
rlm@0:   (my $file) = @_;
rlm@0:   my %map;
rlm@0:   open FILE, "<".$file or die $!;
rlm@0:   for (<FILE>){ chomp; /^(\w+)\W+(\w+)$/; $map{$1} = $2;}
rlm@0:   close FILE;
rlm@0:   return %map;}
rlm@0: 
rlm@0: sub find_beginning{
rlm@0:   ## takes a map representing a linked list and
rlm@0:   ## returns the beginning of that list.
rlm@0:   (my %map) = @_;
rlm@0:   my %val_set = map {$_ => 1} (values %map);
rlm@0:   my $start;
rlm@0:   foreach (keys %map){
rlm@0:     if (!($val_set{$_})){$start = $_;last}}
rlm@0:   return $start;}
rlm@0: 
rlm@0: sub trace_map{
rlm@0:   ## crawls through a map representing a linked-list
rlm@0:   ## and converts it into an actual array structure.
rlm@0:   (my %map) = @_;
rlm@0:   my $position = &find_beginning(%map);
rlm@0:   my @array = ($position);
rlm@0:   while(my $new_position = $map{$position}){
rlm@0:     push (@array, $new_position);
rlm@0:     $position = $new_position;}
rlm@0:   return @array;}
rlm@0: 
rlm@0: 
rlm@0: 
rlm@0: if (defined @ARGV){
rlm@0:   map {print;print"\n";} reverse(trace_map(create_map($ARGV[0])));}