perl - find missing numbers in array

Method 1:

@a = (1,3,4,6);
@c = map $a[$_-1]+1..$a[$_]-1, 1..@a-1;
print join(" ", @c);

Method 2:

@a = (1,3,4,6);
@c = map { ( $a[ $_ - 1 ] + 1 ) .. ( $a[ $_ ] - 1 ) } 1 .. $#a;
print @c;

Method 3:

@a = (1,2,4,6);

push @b, $a[ $_ ] +1 .. $a[ $_+1 ] -1 for 0 .. $#a-1;
print @b;

Method 4:

@a = (1,2,4,6);
@b = do {$i = 0;
    print grep { $_ == $a[ $i ] ? ++$i && 0 : 1 } $a[ 0 ] .. $a[ -1  ];

}

Method 5:

@a = (1,9,4,6);
$i = 0;
for ($c=$a[0]; $c<=$a[$#a]; $c++) {
  if ($c == $a[$i) {    $i++;
  } else {
   print " $c\n";
  }
}

Method 6:

@a = (1,9,4,6);
@b = grep { $var=$_; not grep $var==$_, @a } $a[0]..$a[$#a];
print @b;

Method 7:

@a = ( 1, 3, 4);
%h = map { $_ => 1 } @a;
foreach $i ( $a[0]..$a[-1]) {
if ( ! defined @h{$i} ) {
push @b, $i;
}
}
print @b;

Method 8:

@a = (1 .. 10);
@b = (1, 2, 4, 7, 8, 9);
@c = ();
$i = 0;
for (@a) {
push @c, $_
unless $b[$i] == $_ and ++$i;
}

print @c;

Method 9:

@b=();
@a=(1,3,5);
@h{@a} = ();
foreach $i (11..15) {
    push(@b, $i) unless exists $h{$i};
}
print @b;

Method 10:

perl -lne '@a=(1..6); @b=(1..2,5..6); @c{@a}=(); delete @c{@b}; print for keys %c;';