Add problem 2309: Greatest English Letter in Upper and Lower Case

src/lib.rs

@@ -1714,6 +1714,7 @@ pub mod problem_2300_successful_pairs_of_spells_and_potions;
 pub mod problem_2302_count_subarrays_with_score_less_than_k;
 pub mod problem_2303_calculate_amount_paid_in_taxes;
 pub mod problem_2305_fair_distribution_of_cookies;
+pub mod problem_2309_greatest_english_letter_in_upper_and_lower_case;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_2309_greatest_english_letter_in_upper_and_lower_case/iterative.rs

@@ -0,0 +1,31 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::num::NonZeroU64;
+
+impl Solution {
+    pub fn greatest_letter(s: String) -> String {
+        let state = s.bytes().fold(0, |state, c| state | 1 << (c - b'A'));
+
+        NonZeroU64::new(state & (state >> (b'a' - b'A'))).map_or(String::new(), |state| {
+            char::from(b'A' + 63 - state.leading_zeros() as u8).to_string()
+        })
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn greatest_letter(s: String) -> String {
+        Self::greatest_letter(s)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2309_greatest_english_letter_in_upper_and_lower_case/mod.rs

@@ -0,0 +1,18 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn greatest_letter(s: String) -> String;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [("lEeTcOdE", "E"), ("arRAzFif", "R"), ("AbCdEfGhIjK", "")];
+
+        for (s, expected) in test_cases {
+            assert_eq!(S::greatest_letter(s.to_string()), expected);
+        }
+    }
+}