How to count the number of words only using string methods using a more efficient regex

Input data
You will read the text of the email from the keyboard. It can span multiple lines and contains only lowercase letters of the English alphabet and spaces.

Output data
A single integer will be displayed, representing the number of distinct words in the email

limitation
The text does not contain more than 100,000 words, and each word can contain up to 25 characters.

Input data:
thanks for the list of shopping
Is helpful
thanks

Output data:
7

What I have tried:

Hi, welcome to the Ranch!

What does your program output? How does that differ from what you expect?

p.s. You'll see a "Code" button in the post editor that is good for presenting code as it formats it nicely to be easy to read. I've done it for you this time as you can see.

Welcome to CodeRanch!

Why do you need to replace the call to split()? Is it a requirement that you use regular expressions?

Why are you printing the number of words minus 1? Presumably because otherwise your output doesn't match the expected output for the given input data. However, you should solve it in a different way. The assignment says that you should print the number of distinct words in the email, meaning you must ignore words that you've already seen.

"Is it a requirement that you use regular expressions?" - Yes
"Why are you printing the number of words minus 1?" - my mistake, I fix it.
"Presumably because otherwise your output doesn't match the expected output for the given input data."- Exactly. I receive a wrong answer at the last test when I'm submitting my solution on the platform where I'm learning.

String split() takes a regular expression, and " " is technically a valid regular expression

i'm confused.  Granted it's early...but...

Input data:
thanks(1) for(2) the(3) list(4) of(5) shopping(6)
Is(7) helpful(8)
thanks(duplicate of 1)

Output data:
7

Shouldn't the output be 8?

Good spot Fred. Funny how the rest of us never even thought to question the question.

That was my first thought as well, but then I realized that with 'distinct' the unique words were meant.

so since "thanks" is repeated, it doesn't count at all?  

Also, how should we count "Is"?  the specs say we will only get lower case letters, but that has a capital "I".  

Welcome to the Ranch (again)

Tim Cooke wrote:. . . " " is technically a valid regular expression

Yes, it is. But that depends on the words being separated by single spaces; if there are multiple spaces or line ends, that will give you the wrong answer.I suggest you try a hash set instead of a tree set unless you need the words sorted. Why did youi use − 1 in line 23?