Perl:

#!/usr/bin/perl
use strict;
use warnings;
my %data;
while (<>) {
    chomp;
    if (m/(\w\d+)(\w)/) {
        my $key = $1;
        my $new = $2;
        if (defined $data{$key}) {
            $data{$key} .= "/$new";
        }
        else {
            $data{$key} = $new;
        }
    }
}
while (my ($key, $aa) = each %data) {
    print "$key$aa\n";
}

Test:

$ perl comb.pl < list.txt
A1P/F/C
D4M/S
N6G/L

python solution

from collections import defaultdict
result = defaultdict(str)
for line in open("input.txt").readlines():
  line = line.strip()
  result[line[:2]] = "/".join([result[line[:2]],line[-1]])
with open("output.txt","a") as file:
  for first,second in result.items():
    file.write(first+second[1:]+"\n")