Finish day 10

1 files changed, 67 insertions, 0 deletions

diff --git a/aoc-2020-gleam/src/days/day10.gleam b/aoc-2020-gleam/src/days/day10.gleam
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+import gleam/io
+import gleam/int
+import gleam/list
+import gleam/bool
+import ext/listx
+import ext/pairx
+import ext/genericx as genx
+import ext/resultx as resx
+import util/input_util
+import util/cache.{Cache}
+
+const outlet_joltage = 0
+
+const max_increase = 3
+
+fn process_adapters(numbers: List(Int)) -> List(Int) {
+  let numbers = list.sort(numbers, by: int.compare)
+
+  let device_joltage =
+    numbers
+    |> list.last
+    |> resx.assert_unwrap
+    |> int.add(max_increase)
+
+  list.flatten([[outlet_joltage], numbers, [device_joltage]])
+}
+
+fn part1(numbers: List(Int)) -> Int {
+  let adapters = process_adapters(numbers)
+  let diffs =
+    adapters
+    |> list.window_by_2
+    |> list.map(with: pairx.difference)
+
+  let ones = listx.count(diffs, satisfying: genx.equals(_, 1))
+  let threes = listx.count(diffs, satisfying: genx.equals(_, 3))
+  ones * threes
+}
+
+fn arrangements(number: Int, adapters: List(Int), cache: Cache(Int, Int)) -> Int {
+  use <- bool.guard(when: number == 0, return: 1)
+  use <- bool.guard(when: !list.contains(adapters, number), return: 0)
+  use <- cache.memoize(with: cache, this: number)
+
+  list.range(from: 1, to: max_increase)
+  |> list.map(with: fn(j) { arrangements(number - j, adapters, cache) })
+  |> int.sum
+}
+
+fn part2(numbers: List(Int)) -> Int {
+  let adapters = process_adapters(numbers)
+  let device_joltage = resx.assert_unwrap(list.last(adapters))
+  use cache <- cache.create()
+  arrangements(device_joltage, adapters, cache)
+}
+
+pub fn run() -> Nil {
+  let test = input_util.read_numbers("test10")
+  let assert 220 = part1(test)
+  let assert 19_208 = part2(test)
+
+  let input = input_util.read_numbers("day10")
+  io.debug(part1(input))
+  io.debug(part2(input))
+
+  Nil
+}