Fellow monks,

I have a following problem. Given a string [ATCGN], where series of N is considered as "gap", I would like to obtain the last position of each gap segment. Now the position is in reverse form, see example below:

Example 1: 
   109876543210
    GNNTCGANNTT
      *     *

return value 2 and 8

[download]
Example 2: 
   109876543210
    GAATCGNNNTT
            *

return value 2

[download]
Example 3: 
   109876543210
    GANNCGNNNNN
       *      *

return value 0 and 7

[download]
Can any body advice how can I go about this? I am stuck with my code below: 
my $str = "GNNTCGANNTT";
my @char_arr = split (//,$str);
my $slen = length $str;

foreach my $id (0 .. $#char) {
   if ($str[$id] =~ /N/gi) {
     # not sure how to go from here
    }
}

[download]
And my hopeless approach above also seem very slow. I need to run these process in a speedy manner, as they are many such strings need to be processed.

Regards,
Edward

In reply to Identifying Reverse Position of Specific Character in a String by monkfan

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