argv = ARGV[0]; i = 1; a = ("A".."Z").to_a; j = 0
a.each { |part|
	if part == argv
		j = i+1
	end
	i += 1
}
i = 1; k = 0; l = j-1
while i < j
	print (" "*l)
	i.times do
		print "#{a[j-(j-k)]}"; k += 1
	end
	(i-1).times do
		print "#{a[j-(j-(k-2))]}"; k -= 1
	end
	puts; i+=1; k = 0; l -= 1
end

athelstan@127.0.0.1:~$ ruby Buchstabenpyramide.rb O
               A
              ABA
             ABCBA
            ABCDCBA
           ABCDEDCBA
          ABCDEFEDCBA
         ABCDEFGFEDCBA
        ABCDEFGHGFEDCBA
       ABCDEFGHIHGFEDCBA
      ABCDEFGHIJIHGFEDCBA
     ABCDEFGHIJKJIHGFEDCBA
    ABCDEFGHIJKLKJIHGFEDCBA
   ABCDEFGHIJKLMLKJIHGFEDCBA
  ABCDEFGHIJKLMNMLKJIHGFEDCBA
 ABCDEFGHIJKLMNONMLKJIHGFEDCBA