3 files changed, 38 insertions, 5 deletions
diff --git a/aoc-2020-gleam/src/ext/intx.gleam b/aoc-2020-gleam/src/ext/intx.gleam
index 077b4f2..5c9bcc0 100644
--- a/aoc-2020-gleam/src/ext/intx.gleam
+++ b/aoc-2020-gleam/src/ext/intx.gleam
@@ -1,4 +1,5 @@
 import gleam/int
+import gleam/bool
 import gleam/order.{Eq, Gt, Lt}
 
 pub fn is_between(number: Int, min: Int, and max: Int) {
@@ -9,7 +10,7 @@ pub fn ceil_divide(dividend: Int, by divisor: Int) -> Int {
   { dividend + divisor - 1 } / divisor
 }
 
-fn gcd(a: Int, b: Int) -> Int {
+pub fn gcd(a: Int, b: Int) -> Int {
   case b == 0 {
     True -> a
     False -> gcd(b, a % b)
@@ -22,3 +23,15 @@ pub fn lcm(a: Int, b: Int) -> Int {
     Lt -> { b / gcd(a, b) } * a
   }
 }
+
+fn do_reverse_bits(val: Int, rev: Int, length: Int) -> Int {
+  use <- bool.guard(when: length == 0, return: rev)
+  let lsb = int.bitwise_and(val, 1)
+  let val = int.bitwise_shift_right(val, 1)
+  let rev = int.bitwise_shift_left(rev, 1)
+  do_reverse_bits(val, int.bitwise_or(rev, lsb), length - 1)
+}
+
+pub fn reverse_bits(val: Int, length: Int) -> Int {
+  do_reverse_bits(val, 0, length)
+}
diff --git a/aoc-2020-gleam/src/ext/iteratorx.gleam b/aoc-2020-gleam/src/ext/iteratorx.gleam
index 0e59f17..6c7838d 100644
--- a/aoc-2020-gleam/src/ext/iteratorx.gleam
+++ b/aoc-2020-gleam/src/ext/iteratorx.gleam
@@ -1,3 +1,6 @@
+import gleam/int
+import gleam/result as res
+import gleam/dict.{type Dict}
 import gleam/iterator.{type Iterator, Next} as iter
 
 pub fn length(iterator: Iterator(a)) -> Int {
@@ -11,6 +14,19 @@ pub fn count(iterator: Iterator(a), satisfying predicate: fn(a) -> Bool) -> Int
   |> length
 }
 
+pub fn counts(iterator: Iterator(a)) -> Dict(a, Int) {
+  iterator
+  |> iter.fold(from: dict.new(), with: fn(acc, value) {
+    acc
+    |> dict.insert(
+      value,
+      dict.get(acc, value)
+      |> res.unwrap(or: 0)
+      |> int.add(1),
+    )
+  })
+}
+
 pub fn filter_map(
   iterator: Iterator(a),
   with mapper: fn(a) -> Result(b, c),
@@ -25,8 +41,5 @@ pub fn filter_map(
 }
 
 pub fn unfold_infinitely(from state: a, with fun: fn(a) -> a) -> Iterator(a) {
-  iter.unfold(
-    from: state,
-    with: fn(s) { Next(element: s, accumulator: fun(s)) },
-  )
+  iter.unfold(from: state, with: fn(s) { Next(element: s, accumulator: fun(s)) })
 }
diff --git a/aoc-2020-gleam/src/ext/listx.gleam b/aoc-2020-gleam/src/ext/listx.gleam
index 2ca8648..0a3d7c3 100644
--- a/aoc-2020-gleam/src/ext/listx.gleam
+++ b/aoc-2020-gleam/src/ext/listx.gleam
@@ -1,6 +1,7 @@
 import gleam/pair
 import gleam/iterator as iter
 import gleam/result as res
+import gleam/dict.{type Dict}
 import ext/iteratorx as iterx
 
 pub fn count(list: List(a), satisfying predicate: fn(a) -> Bool) -> Int {
@@ -9,6 +10,12 @@ pub fn count(list: List(a), satisfying predicate: fn(a) -> Bool) -> Int {
   |> iterx.count(satisfying: predicate)
 }
 
+pub fn counts(list: List(a)) -> Dict(a, Int) {
+  list
+  |> iter.from_list
+  |> iterx.counts
+}
+
 fn set_helper(list: List(a), value: a, index: Int, counter: Int) -> List(a) {
   case list {
     [] -> []