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    %hash = map { getkey($_) => $_ } @array;

    %hash = ();
    foreach $_ (@array) {
        $hash{getkey($_)} = $_;
    }

  my %res = map {
    $_ => do {
...
    } if !$res{$_};
  } @words;

  my %res;
  my @res = map {
...
    } if !$res{$_};
  } @words;
  %res = @res;

  my %res;
  %res = @_ =map {
...
        $re;
    } if !$res{$_};
  } @words;