Another solution is to use bitmaps:

$ perl -e'
$x = q[A 1  2  
A 7  10 
A 15 20 
B 3  5  
B 11 15  
C 5  10  
D 10 20  
];

open my $fh, q[<], \$x or die "Cannot open \$x: $!";

my ( $mask, %data, $max );
while ( <$fh> ) {
    my ( $key, @vals ) = split;
    for my $val ( @vals ) {
        vec( $mask, $val, 1 ) = vec( $data{ $key }, $val, 1 ) = 1;
        $max = $val if $max < $val;
        }
    }

my @vals;
for my $val ( 0 .. $max ) {
    push @vals, $val if vec $mask, $val, 1;
    }

my $width = length $vals[ -1 ];
printf q[ID] . ( " %${width}d" x @vals ) . "\n", @vals;

for my $key ( sort keys %data ) {
    printf q[%-2s], $key;
    for my $val ( @vals ) {
        printf q[ %*d], $width, vec $data{ $key }, $val, 1;
        }
    print "\n";
    }
'
ID  1  2  3  5  7 10 11 15 20
A   1  1  0  0  1  1  0  1  1
B   0  0  1  1  0  0  1  1  0
C   0  0  0  1  0  1  0  0  0
D   0  0  0  0  0  1  0  0  1
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