static Span <LetterPair> GetAllPairs(string s)
{
Span <LetterPair> pairs = new LetterPair[s.Length - 1];//cannot stackalloc here, use stackalloc if inlining
int pos = 0;
for (int i = 0; i < s.Length - 1; i++)
{
if (s[i] != ' ' && s[i + 1] != ' ')
{
pairs[pos++] = new LetterPair(s[i], s[i + 1]);
}
}
return(pairs.Slice(0, pos));
}
public static float CompareStrings(string str1, string str2, bool caseSensitive)
{
if (string.IsNullOrWhiteSpace(str1) || string.IsNullOrWhiteSpace(str2))
{
return(0);
}
Span <LetterPair> pairs1 = GetAllPairs(caseSensitive ? str1 : str1.ToUpperInvariant());
Span <LetterPair> pairs2 = GetAllPairs(caseSensitive ? str2 : str2.ToUpperInvariant());
if (pairs1.Length == 0 || pairs2.Length == 0)
{
return(0);
}
else
{
bool[] usedPairs = new bool[pairs2.Length];
int intersection = 0;
int union = pairs1.Length + pairs2.Length;
for (int i = 0; i < pairs1.Length; i++)
{
LetterPair pair1 = pairs1[i];
for (int j = 0; j < pairs2.Length; j++)
{
if (!usedPairs[j] && pair1 == pairs2[j])
{
intersection++;
usedPairs[j] = true;
break;
}
}
}
return((2f * intersection) / union);
}
