use strict; # just kidding
my%hat;my@cat=split/ /,<DATA>;
while(@cat){
  my($cat=>$hat)=splice@cat,0,2;
  $hat{$cat}=$hat>$hat{$cat}?$hat:$hat{$cat};
}
print join" ",%hat; # and that was that
__DATA__
a.txt 4 b.txt 3 z.txt 1 a.txt 5 b.txt 2 b.txt 4 z.txt 2