From c9f008521c8b630de4a3ee8edb5f68f62884a531 Mon Sep 17 00:00:00 2001
From: EFanZh <efanzh@gmail.com>
Date: Wed, 6 Nov 2024 22:38:54 +0800
Subject: [PATCH] Add problem 2309: Greatest English Letter in Upper and Lower
 Case

---
 src/lib.rs                                    |  1 +
 .../iterative.rs                              | 31 +++++++++++++++++++
 .../mod.rs                                    | 18 +++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 src/problem_2309_greatest_english_letter_in_upper_and_lower_case/iterative.rs
 create mode 100644 src/problem_2309_greatest_english_letter_in_upper_and_lower_case/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index 56ffcc55..29fda6fe 100644
--- a/src/lib.rs
+++ b/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;
diff --git a/src/problem_2309_greatest_english_letter_in_upper_and_lower_case/iterative.rs b/src/problem_2309_greatest_english_letter_in_upper_and_lower_case/iterative.rs
new file mode 100644
index 00000000..58219324
--- /dev/null
+++ b/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>();
+    }
+}
diff --git a/src/problem_2309_greatest_english_letter_in_upper_and_lower_case/mod.rs b/src/problem_2309_greatest_english_letter_in_upper_and_lower_case/mod.rs
new file mode 100644
index 00000000..3403506b
--- /dev/null
+++ b/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);
+        }
+    }
+}