Private IList<Range>[] GetRanges(string str1, string str2)

Question

Private IList<Range>[] GetRanges(string str1, string str2)

{
if (string.IsNullOrEmpty(str1) || string.IsNullOrEmpty(str2)) throw new Exception("Nullable value`s");
List<Range>[] ret = {new List<Range>(),new List<Range>()};
if (str1.Length > str2.Length) str1 = str1.Substring(0, str2.Length);
if (str2.Length > str1.Length) str2 = str1.Substring(0, str1.Length);
var tmp = str1.Select((t, i) => t == str2[i]).ToList();
for (int i = 0, x=0, len=1; i < tmp.Count-1; i++,len++)
if(tmp[i]!=tmp[i+1])
{
ret[tmp[i]?0:1].Add(new Range{X=x,Lenth = len});
x = i + 1;
len = 0;
}
return ret;
}