solve(2351): implement solution using hash set

Author: kallydev

src/solutions/_2351_first_letter_to_appear_twice.rs

@@ -0,0 +1,25 @@
+use std::collections::HashSet;
+
+use crate::solutions::Solution;
+
+impl Solution {
+    pub fn repeated_character(s: String) -> char {
+        let mut hash_set = HashSet::new();
+
+        for c in s.chars() {
+            if hash_set.contains(&c) {
+                return c;
+            }
+
+            hash_set.insert(c);
+        }
+
+        unreachable!()
+    }
+}
+
+#[test]
+fn test() {
+    assert_eq!(Solution::repeated_character("abccbaacz".to_owned()), 'c');
+    assert_eq!(Solution::repeated_character("abcdd".to_owned()), 'd');
+}

src/solutions/mod.rs

@@ -4,6 +4,7 @@ pub mod _0020_valid_parentheses;
 pub mod _0026_remove_duplicates_from_sorted_array;
 pub mod _0027_remove_element;
 pub mod _1848_minimum_distance_to_the_target_element;
+pub mod _2351_first_letter_to_appear_twice;
 pub mod _3046_split_the_array;
 pub mod _3151_special_array_i;
 pub mod _3174_clear_digits;