diff --git a/README.md b/README.md
index 8c0e2e8..f22445d 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,7 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 118. Pascal's Triangle                          | [Link](https://leetcode.com/problems/pascals-triangle/)                           | [Link](./lib/easy/118_pascals_triangle.dart)                           |
 | 263. Ugly Number                                | [Link](https://lettcode.com/problems/ugly-number/)                                | [Link](./lib/easy/263_ugly_number.dart)                                |
 | 500. Keyboard Row                               | [Link](https://leetcode.com/problems/keyboard-row/)                               | [Link](./lib/easy/500_keyboard_row.dart)                               |
+| 3120. Count the Number of Special Characters I  | [Link](https://leetcode.com/problems/count-the-number-of-special-characters-i/)   | [Link](./lib/easy/3120_count_the_number_of_special_characters_i.dart)  |
 | 3280. Convert Date to Binary                    | [Link](https://leetcode.com/problems/convert-date-to-binary/)                     | [Link](./lib/easy/3280_convert_date_to_binary.dart)                    |
 | 3340. Check Balanced String                     | [Link](https://leetcode.com/problems/check-balanced-string/)                      | [Link](./lib/easy/3340_check_balanced_string.dart)                     |
 | 3516. Find Closest Person                       | [Link](https://leetcode.com/problems/find-closest-person/)                        | [Link](./lib/easy/3516_find_closest_person.dart)                       |
diff --git a/lib/easy/3120_count_the_number_of_special_characters_i.dart b/lib/easy/3120_count_the_number_of_special_characters_i.dart
new file mode 100644
index 0000000..f569113
--- /dev/null
+++ b/lib/easy/3120_count_the_number_of_special_characters_i.dart
@@ -0,0 +1,26 @@
+class Solution {
+  int numberOfSpecialChars(String word) {
+    final lower = List.filled(26, 0);
+    final upper = List.filled(26, 0);
+
+    for (var i = 0; i < word.length; i += 1) {
+      final char = word[i];
+
+      if (char.compareTo('a') >= 0 && char.compareTo('z') <= 0) {
+        lower[char.codeUnitAt(0) - 'a'.codeUnitAt(0)] += 1;
+      } else {
+        upper[char.codeUnitAt(0) - 'A'.codeUnitAt(0)] += 1;
+      }
+    }
+
+    var result = 0;
+
+    for (var i = 0; i < upper.length; i += 1) {
+      if (lower[i] > 0 && upper[i] > 0) {
+        result += 1;
+      }
+    }
+
+    return result;
+  }
+}
diff --git a/pubspec.yaml b/pubspec.yaml
index 0801393..c32ba70 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: leetcode_dart
 description: Some solved problems from https://leetcode.com on Dart
-version: 1.0.7
+version: 1.0.8
 homepage: https://github.com/fartem/leetcode-dart
 
 environment:
diff --git a/test/easy/3120_count_the_number_of_special_characters_i_test.dart b/test/easy/3120_count_the_number_of_special_characters_i_test.dart
new file mode 100644
index 0000000..1c20688
--- /dev/null
+++ b/test/easy/3120_count_the_number_of_special_characters_i_test.dart
@@ -0,0 +1,41 @@
+import 'package:leetcode_dart/easy/3120_count_the_number_of_special_characters_i.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group(
+    'Example tests',
+    () {
+      final solution = Solution();
+
+      test(
+        '3',
+        () => expect(
+          3,
+          solution.numberOfSpecialChars(
+            'aaAbcBC',
+          ),
+        ),
+      );
+
+      test(
+        '0',
+        () => expect(
+          0,
+          solution.numberOfSpecialChars(
+            'abc',
+          ),
+        ),
+      );
+
+      test(
+        '1',
+        () => expect(
+          1,
+          solution.numberOfSpecialChars(
+            'abBCab',
+          ),
+        ),
+      );
+    },
+  );
+}