Efficient way to find Frequency of a character in a String in java : O(n)

Question

In a recent interview I was asked to write the below program. Find out the character whose frequency is minimum in the given String ? So I tried by iterating through the string

Answer 1

I'd do it the following way as it involves the fewest lines of code:

character you wish to want to know frequency of: "_"
String "this_is_a_test"

String testStr = "this_is_a_test";
String[] parts = testStr.split("_"); //note you need to use regular expressions here
int freq = parts.length -1;

You may find weird things happen if the string starts or ends with the character in question, but I'll leave it to you to test for that.