Я бы использовал оператор switch :
public string RideCombination(ReturnParameter retor)
{
switch ($"{retor.v1}{retor.v2}{retor.v3}")
{
case "AbC":
return "valid 1 ";
case "CAC":
return "valid 2 ";
case "DTC":
return "valid 3 ";
case "ABC":
return "valid 4 ";
default:
return "no match!";
}
}
или Словарь для поиска в постоянном времени:
Dictionary<string, string> lookup = new Dictionary<string, string>
{
{ "AbC", "valid 1 "},
{ "CAC", "valid 2 "},
{ "DTC", "valid 3 "},
{ "ABC", "valid 4 "}
};
return lookup[$"{retor.v1}{retor.v2}{retor.v3}"];