From da59603764532ead4ba804af1ec94a964172afa0 Mon Sep 17 00:00:00 2001
From: Nat Quayle Nelson <natquaylenelson@gmail.com>
Date: Fri, 11 Dec 2020 21:38:16 -0700
Subject: [PATCH] Solve arrangement count for AOC Day 10pt2

---
 projects/aoc/src/year2020/Adapters.hx    |  1 +
 projects/aoc/src/year2020/Adapters.kiss  | 13 ++++++++++++-
 projects/aoc/src/year2020/Solutions.hx   |  1 +
 projects/aoc/src/year2020/Solutions.kiss |  5 +++--
 4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/projects/aoc/src/year2020/Adapters.hx b/projects/aoc/src/year2020/Adapters.hx
index c421ebf1..020760ae 100644
--- a/projects/aoc/src/year2020/Adapters.hx
+++ b/projects/aoc/src/year2020/Adapters.hx
@@ -1,5 +1,6 @@
 package year2020;
 
+import haxe.Int64;
 import kiss.Prelude;
 import year2020.Util;
 
diff --git a/projects/aoc/src/year2020/Adapters.kiss b/projects/aoc/src/year2020/Adapters.kiss
index 7077ff9d..fe3f19ce 100644
--- a/projects/aoc/src/year2020/Adapters.kiss
+++ b/projects/aoc/src/year2020/Adapters.kiss
@@ -8,4 +8,15 @@
                 (if (dist.exists num)
                         (+ 1 (dictGet dist num))
                     1)))
-        dist))
\ No newline at end of file
+        dist))
+
+(defun arrangementCount [:kiss.List<Int> ratings startingIndex]
+    (if (= startingIndex (- ratings.length 1)) 1
+        (let [&mut :Int64 sum 0
+                startingRating (nth ratings startingIndex)
+                potentialNextAdapters (filter
+                                            (for i (range (+ 1 startingIndex) (+ 4 startingIndex)) i)
+                                            (lambda [index] (and (< index ratings.length) (<= (nth ratings index) (+ 3 startingRating)))))]
+            (doFor subCount (map potentialNextAdapters (arrangementCount.bind ratings))
+                (set sum (Int64.add sum subCount)))
+            sum)))
diff --git a/projects/aoc/src/year2020/Solutions.hx b/projects/aoc/src/year2020/Solutions.hx
index 92cda945..b145d342 100644
--- a/projects/aoc/src/year2020/Solutions.hx
+++ b/projects/aoc/src/year2020/Solutions.hx
@@ -1,6 +1,7 @@
 package year2020;
 
 import haxe.ds.Map;
+import haxe.Int64;
 import StringTools;
 import kiss.Prelude;
 import kiss.Stream;
diff --git a/projects/aoc/src/year2020/Solutions.kiss b/projects/aoc/src/year2020/Solutions.kiss
index 39efef93..5c1099a5 100644
--- a/projects/aoc/src/year2020/Solutions.kiss
+++ b/projects/aoc/src/year2020/Solutions.kiss
@@ -116,8 +116,9 @@
         (assert (= 16107959 (+ (apply min tuple) (apply max tuple)))))
 
     // Day 10
-    (let [adapters (Util.readInts "src/year2020/inputs/day10.txt")]
-        (.sort adapters Reflect.compare)
+    (assert (Int64.eq 8 (Adapters.arrangementCount (sort [0 22 16 10 15 5 1 11 7 19 6 12 4]) 0)))
+    (assert (Int64.eq 19208 (Adapters.arrangementCount (sort [0 52 28 33 18 42 31 14 46 20 48 47 24 23 49 45 19 38 39 11 1 32 25 35 8 17 7 9 4 2 34 10 3]) 0)))
+    (let [adapters (sort (Util.readInts "src/year2020/inputs/day10.txt"))]
         (adapters.unshift 0)
         (adapters.push (+ 3 (last adapters)))
         (let [diffs (Adapters.differences adapters)