Just a few comments (since I don't really know what algorithm you are trying to implement). First consider using using strict and warnings. And next, on this line:

for(my $i=$m;$i<scalar @a;$i++)
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A more "perlish" way of doing that sort of thing is:

for my $i ($m..$#a)
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And this:

while (($key1, $val1) = each(%num))
{
push(@key,$key1);
push(@val,$val1);
}
}
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Is easier done like this (and they will be in the correct corresponding order):

my @key = keys %num;
my @val = values %num;
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