Challenge 1: Borrow, Don't Move — Possible Solution
====================================================================

fn count_words(s: &String) -> usize {
    s.split_whitespace().count()
}

fn main() {
    let sentence = String::from("the quick brown fox jumps");

    let count1 = count_words(&sentence);
    println!("Word count: {}", count1);

    let count2 = count_words(&sentence);
    println!("Word count again: {}", count2);
}

WHY THIS WORKS AS AN ANSWER
------------------------------
count_words takes &String — an immutable REFERENCE, not an owned
String — so calling it never moves sentence's ownership away from
main, exactly this chapter's fix for Chapter 3's takes_ownership
problem.

Because sentence is only ever borrowed (never moved), it remains
fully valid after the first call — proven directly by calling
count_words(&sentence) a SECOND time, which would be a compile error
("value used after move") if the first call had taken ownership
instead of borrowing. Both calls succeed and both print the same
count, since split_whitespace().count() simply reads the string's
contents without needing to own or modify it.