just for fun:

my @data = ([1,30], [40, 50], [25, 37], [60, 70], [50, 60], [65, 99]);

my @data = map { my ($a, $b) = split/:/; [$a, $b]; }
        split / /,
        join ':',
        map { my @d = split / /; scalar @d > 1 && $d[0]>=$d[1] ? ():"@
+d" }
        split /:/,
        join ' ',
        map {"$_->[0]:$_->[1]"}
        sort {$a->[0] <=> $b->[0]}
        @data;
[download]

Oha