Description:

Compare two strings by comparing the sum of their letter-Values (char-Value).
For comparing treat all letters as UpperCase.

Empty and null-Strings should be treated as they are equal.
If the string contains other characters than letters, treat the whole string as it would be empty.

Examples:

"AD","BC" -> equal

"AD","DD" -> not equal

"gf","FG" -> equal

"zz1","" -> equal

"ZzZz", "ffPFF" -> equal

"kl", "lz" -> not equal

null, "" -> equal

Test Cases:

Test.describe("Basic tests") do
Test.assert_equals(compare("AD", "BC"), true, "\'AD\' vs \'BC\'")
Test.assert_equals(compare("AD", "DD"), false, "\'AD\' vs \'DD\'")
Test.assert_equals(compare("gf", "FG"), true, "\'gf\' vs \'FG\'")
Test.assert_equals(compare("Ad", "DD"), false, "\'Ad\' vs \'DD\'")
Test.assert_equals(compare("zz1", ""), true, "\'zz1\' vs \'\'")
Test.assert_equals(compare("ZzZz", "ffPFF"), true, "\'ZzZz\' vs \'ffPFF\'")
Test.assert_equals(compare("kl", "lz"), false, "\'kl\' vs \'lz\'")
Test.assert_equals(compare(nil, ""), true, "\'<null>\' vs \'\'")
Test.assert_equals(compare("!!", "7476"), true, "\'!!\' vs \'7476\'")
Test.assert_equals(compare("##", "1176"), true, "\'##\' vs \'1176\'")
end

Solution:

def compare(s1,s2)
  alphabet = ("A".."Z").to_a
  s1_arr = s1.upcase.split(//)
  s2_arr = s2.upcase.split(//)
  s1_val = 0
  for count in 0...s1_arr.length
      if !(alphabet.include? s1_arr[count]) 
        s1_val = 0
        break
      end  
      for counter in 0...26
        if s1_arr[count] == alphabet[counter]
          #s1_val += counter+1 
          s1_val += alphabet[counter].ord 
        end
      end
  end
  s2_val = 0
  for count in 0...s2_arr.length
      if !(alphabet.include? s2_arr[count]) 
        s2_val = 0
        break
      end       
      for counter in 0...26
        if s2_arr[count] == alphabet[counter]
          #s2_val += counter+1
          s2_val += alphabet[counter].ord 
        end
      end
  end
s1_val == s2_val 
end