diff --git a/src/day_02.gleam b/src/day_02.gleam
new file mode 100644
index 0000000..16d4b95
--- /dev/null
+++ b/src/day_02.gleam
@@ -0,0 +1,61 @@
+import gleam/bool
+import gleam/int
+import gleam/list
+import gleam/string
+
+pub type Range {
+  Range(min: Int, max: Int)
+}
+
+pub fn format_input(input: String) -> List(Range) {
+  input
+  |> string.split(",")
+  |> list.map(fn (range) {
+    let assert [min, max] = 
+      range
+      |> string.replace(each: "\n", with: "")
+      |> string.split("-")
+    let assert Ok(min_int) = int.parse(min)
+    let assert Ok(max_int) = int.parse(max)
+
+    Range(min: min_int, max: max_int)
+  })
+}
+
+fn is_repeated(number: String) -> Bool {
+  let number_length = string.length(number)
+
+  use <- bool.guard(when: number_length % 2 != 0, return: False)
+
+  number
+  |> string.slice(at_index: number_length / 2, length: number_length)
+  |> string.starts_with(number, _)
+}
+
+fn find_duplicates(range: Range, acc: List(Int)) -> List(Int) {
+  let Range(min: min, max: max) = range
+
+  use <- bool.guard(when: min > max, return: acc)
+
+  case min |> int.to_string |> is_repeated {
+    True -> find_duplicates(
+      Range(min: min + 1, max: max),
+      [min, ..acc]
+    )
+    False -> find_duplicates(
+      Range(min: min + 1, max: max),
+      acc
+    )
+  }
+}
+
+pub fn calculate_duplicates(ranges: List(Range)) -> Int {
+  ranges
+  |> list.fold(0, fn (acc, range) {
+    let arr = range
+    |> find_duplicates([])
+    |> list.fold(0, fn (a, b) { a + b })
+
+    acc + arr
+  })
+}
diff --git a/test/day_02_test.gleam b/test/day_02_test.gleam
new file mode 100644
index 0000000..c9a60e2
--- /dev/null
+++ b/test/day_02_test.gleam
@@ -0,0 +1,36 @@
+import simplifile
+import day_02.{Range}
+
+pub fn read_input_test() {
+  assert "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124"
+    |> day_02.format_input
+    == [
+      Range(min: 11, max: 22),
+      Range(min: 95, max: 115),
+      Range(min: 998, max: 1012),
+      Range(min: 1188511880, max: 1188511890),
+      Range(min: 222220, max: 222224),
+      Range(min: 1698522, max: 1698528),
+      Range(min: 446443, max: 446449),
+      Range(min: 38593856, max: 38593862),
+      Range(min: 565653, max: 565659),
+      Range(min: 824824821, max: 824824827),
+      Range(min: 2121212118, max: 2121212124),
+    ]
+}
+
+pub fn calculate_duplicates_test() {
+  assert "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124"
+    |> day_02.format_input
+    |> day_02.calculate_duplicates
+    == 1227775554
+}
+
+pub fn calculate_duplicates_for_real_test() {
+  let assert Ok(file) = simplifile.read("input/day_02")
+
+  assert file
+    |> day_02.format_input
+    |> day_02.calculate_duplicates
+    == 18595663903
+}