Finish day 9

2 files changed, 23 insertions, 0 deletions

diff --git a/aoc-2020-gleam/src/ext/iteratorx.gleam b/aoc-2020-gleam/src/ext/iteratorx.gleam
index 0ef5d51..65e06f2 100644
--- a/aoc-2020-gleam/src/ext/iteratorx.gleam
+++ b/aoc-2020-gleam/src/ext/iteratorx.gleam
@@ -10,3 +10,16 @@ pub fn count(iterator: Iterator(a), satisfying predicate: fn(a) -> Bool) -> Int
   |> iter.filter(for: predicate)
   |> length
 }
+
+pub fn filter_map(
+  iterator: Iterator(a),
+  with mapper: fn(a) -> Result(b, c),
+) -> Iterator(b) {
+  iterator
+  |> iter.flat_map(with: fn(elem) {
+    case mapper(elem) {
+      Ok(new) -> iter.single(new)
+      Error(_) -> iter.empty()
+    }
+  })
+}
diff --git a/aoc-2020-gleam/src/ext/listx.gleam b/aoc-2020-gleam/src/ext/listx.gleam
index 2d4f4b6..8d20bd6 100644
--- a/aoc-2020-gleam/src/ext/listx.gleam
+++ b/aoc-2020-gleam/src/ext/listx.gleam
@@ -1,4 +1,6 @@
+import gleam/pair
 import gleam/iterator as iter
+import gleam/result as res
 import ext/iteratorx as iterx
 
 pub fn count(list: List(a), satisfying predicate: fn(a) -> Bool) -> Int {
@@ -18,3 +20,11 @@ fn set_helper(list: List(a), value: a, index: Int, counter: Int) -> List(a) {
 pub fn set(list: List(a), value: a, at index: Int) -> List(a) {
   set_helper(list, value, index, 0)
 }
+
+pub fn index_of(list: List(a), value: a) -> Result(Int, Nil) {
+  list
+  |> iter.from_list
+  |> iter.index
+  |> iter.find(one_that: fn(elem) { pair.second(elem) == value })
+  |> res.map(with: pair.first)
+}