From 2e17bfb03417ab1e01d31e1f5d09e94d1cdebdd9 Mon Sep 17 00:00:00 2001
From: Wesley Moore <wes@wezm.net>
Date: Sat, 3 Dec 2022 16:34:01 +1000
Subject: [PATCH] Day 3 part 2

---
 2022/src/days/day_3.gleam | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/2022/src/days/day_3.gleam b/2022/src/days/day_3.gleam
index 33545e8..4eed40d 100644
--- a/2022/src/days/day_3.gleam
+++ b/2022/src/days/day_3.gleam
@@ -1,6 +1,7 @@
 import gleam/int
 import gleam/set
 import gleam/list.{map}
+import gleam/iterator
 import gleam/string
 
 type Rucksack =
@@ -8,15 +9,21 @@ type Rucksack =
 
 pub fn pt_1(input: String) -> Int {
   string.split(input, on: "\n")
-  |> list.map(string.to_graphemes)
-  |> list.map(split_in_half)
-  |> list.map(common_item)
-  |> list.map(priority)
+  |> map(string.to_graphemes)
+  |> map(split_in_half)
+  |> map(common_item)
+  |> map(priority)
   |> int.sum
 }
 
 pub fn pt_2(input: String) -> Int {
-  todo
+  string.split(input, on: "\n")
+  |> map(string.to_graphemes)
+  |> iterator.from_list
+  |> iterator.sized_chunk(3)
+  |> iterator.map(common_item_pt2)
+  |> iterator.map(priority)
+  |> iterator.fold(0, fn(sum, prio) { sum + prio })
 }
 
 fn split_in_half(l: List(String)) -> Rucksack {
@@ -35,6 +42,19 @@ fn common_item(rucksack: Rucksack) -> String {
   common
 }
 
+fn common_item_pt2(sacks: List(List(String))) -> String {
+  assert Ok(inter) =
+    sacks
+    |> map(set.from_list)
+    |> list.reduce(set.intersection)
+  assert 1 = set.size(inter)
+  assert Ok(common) =
+    inter
+    |> set.to_list
+    |> list.first
+  common
+}
+
 // Lowercase item types a through z have priorities 1 through 26.
 // Uppercase item types A through Z have priorities 27 through 52.
 // I can't find a way to get a codepoint or match on a range with Gleam so this