Add problem 2351: First Letter to Appear Twice

src/lib.rs

@@ -1742,6 +1742,7 @@ pub mod problem_2342_max_sum_of_a_pair_with_equal_sum_of_digits;
 pub mod problem_2347_best_poker_hand;
 pub mod problem_2348_number_of_zero_filled_subarrays;
 pub mod problem_2349_design_a_number_container_system;
+pub mod problem_2351_first_letter_to_appear_twice;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_2351_first_letter_to_appear_twice/iterative.rs

@@ -0,0 +1,39 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn repeated_character(s: String) -> char {
+        let mut counts = [false; 26];
+        let mut result = 0;
+
+        for c in s.bytes() {
+            match &mut counts[usize::from(c) - usize::from(b'a')] {
+                state @ false => *state = true,
+                true => {
+                    result = c;
+
+                    break;
+                }
+            }
+        }
+
+        char::from(result)
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn repeated_character(s: String) -> char {
+        Self::repeated_character(s)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2351_first_letter_to_appear_twice/mod.rs

@@ -0,0 +1,18 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn repeated_character(s: String) -> char;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [("abccbaacz", 'c'), ("abcdd", 'd')];
+
+        for (s, expected) in test_cases {
+            assert_eq!(S::repeated_character(s.to_string()), expected);
+        }
+    }
+}