Day 3

src/aoc.gleam

···
 import birl/duration
 import days/day1
 import days/day2
+import days/day3
 import gleam/erlang
 import gleam/int
 import gleam/io
···
     0 -> io.println_error("Invalid day")
     1 -> day1.start()
     2 -> day2.start()
+    3 -> day3.start()
     _ -> io.println("Tried to run day " <> int.to_string(day))
   }
   birl.now()

src/days/day3.gleam

···
+import gleam/float
+import gleam/int
+import gleam/io
+import gleam/list
+import gleam/result
+import gleam/string
+import simplifile
+import utils/utils
+
+pub fn start() -> Nil {
+  let assert Ok(content) = simplifile.read("inputs/day3.txt")
+  let data = parse(content)
+
+  let _ = io.debug(part1(data))
+  let _ = io.debug(part2(data))
+
+  Nil
+}
+
+fn parse(data: String) {
+  string.split(data, "\n")
+  |> list.map(string.to_graphemes)
+  |> list.map(list.map(_, int.parse))
+  |> list.map(list.map(_, result.unwrap(_, 0)))
+}
+
+type LstMaxIdx {
+  LstMaxIdx(idx: Int, value: Int)
+}
+
+fn max_int_from_index(lst: List(Int), start_from: Int, last_offset: Int) {
+  lst
+  |> list.drop(start_from)
+  |> list.index_fold(LstMaxIdx(0, 0), fn(max, num, idx) {
+    case idx >= { list.length(lst) - start_from - last_offset } {
+      True -> max
+      False ->
+        case max.value < num {
+          True -> LstMaxIdx(idx + start_from, num)
+          False -> max
+        }
+    }
+  })
+}
+
+fn part1(data: List(List(Int))) {
+  list.map(data, fn(x) {
+    let first = max_int_from_index(x, 0, 1)
+    let second = max_int_from_index(x, first.idx + 1, 0)
+    first.value * 10 + second.value
+  })
+  |> list.fold(0, int.add)
+}
+
+fn part2(data: List(List(Int))) {
+  let range = utils.create_int_range(0, 12)
+  list.map(data, fn(x) {
+    list.fold(range, #(0, 0), fn(acc, offset) {
+      let res = max_int_from_index(x, acc.1, { 11 - offset })
+      #(
+        acc.0
+          + res.value
+          * {
+          int.power(10, float.subtract({ 12.0 -. 1.0 }, int.to_float(offset)))
+          |> result.unwrap(0.0)
+          |> float.round
+        },
+        res.idx + 1,
+      )
+    }).0
+  })
+  |> list.reduce(int.add)
+  |> result.unwrap(0)
+}