String starts with anything in a set<String>?

Question

I want to see if any of the strings I pass(num) starts with any of the values on my set

  Ex. String num = 456987533;

  Set<String> numValidator = new Set<String>{‘456’,’312’,762’};

Since my num starts with ‘456’ it should come back true.

How can I write this out?

StartsWith does not work because it is only comparing a string and not a set

Answer 1

Unless all of your String prefixes are the same length, you'll need to iterate over the contents of your Set.

  for (String s : numValidator) {
       if (myInputString.startsWith(s)) {
           // do something
       }
  }

However, if all of your prefixes are exactly three characters, you can handle this more simply and make use of Set membership constant-time checking:

Set<String> numValidator = new Set<String>{'456','312','762'};
String myInputString = '312456';

if (numValidator.contains(myInputString.left(3))) {
    System.debug('Found it');
}