Fastest way to check if string contains only digits

Question

I know a few ways how to check this. regex,int.parse,tryparse,looping.

can anyone tell me what is the fastest way to check?

the nee

Answer 1

if it is a single string :

if (str.All(Char.IsDigit))
{
  // string contains only digits
}

if it is a list of strings :

if (lstStr.All(s => s.All(Char.IsDigit)))
{
  // List of strings contains only digits
}