private static string FindMaxMergePair(CharInfo ci, int idx, char[] result, StringChar lastSuccessfulChar)
{
if (idx == result.Length)
{
return(new string(result));
}
string s = null;
StringChar lastFailedChar = null;
while (s == null)
{
StringChar sc = ci.RemoveMaxPossibleChar(lastSuccessfulChar, lastFailedChar);
if (sc == null)
{
return(null);
}
result[idx] = sc.c;
s = FindMaxMergePair(ci, idx + 1, result, sc);
if (s == null)
{
lastFailedChar = sc;
ci.AddChar(sc);
}
}
return(s);
}
