From 84a210170fd64fefce688c927531a51f886d8515 Mon Sep 17 00:00:00 2001
From: Daniel Flanagan <daniel@lyte.dev>
Date: Thu, 10 Dec 2020 12:37:10 -0600
Subject: [PATCH] Day 10 part 2 and cleanup

---
 2020/src/day10.nim | 25 ++++++++++++++++++++++---
 2020/src/day9.nim  |  2 +-
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/2020/src/day10.nim b/2020/src/day10.nim
index 8d7586e..9136852 100644
--- a/2020/src/day10.nim
+++ b/2020/src/day10.nim
@@ -1,4 +1,4 @@
-import streams, input_helpers, algorithm, sequtils
+import streams, input_helpers, algorithm, sequtils, math
 
 proc part1*(s: Stream): int =
   var d1 = 0
@@ -11,6 +11,25 @@ proc part1*(s: Stream): int =
       else: discard
   d1 * d3
 
-
 proc part2*(s: Stream): int =
-  0
+  result = 1
+  var nums = @[0].concat(toSeq(s.asInts).sorted)
+  nums = nums.concat @[nums.max + 3]
+  var l,r = 0
+  while l < nums.len:
+    r = l
+    while r < (nums.len-1) and nums[r+1] - nums[r] == 1: inc r
+    let ln = r+1-l
+    case ln:
+      of 0..2: discard
+      of 3: result *= 2
+      else: result *= 1 + (ln - 2) + (ln - 2).fac.div(2)
+    l = r + 1
+
+# needed the tests on this one - math was a doozy
+const t2 = "1\n4\n5\n6\n7\n10\n11\n12\n15\n16\n19".newStringStream().part2()
+const t = ("1\n2\n3\n4\n7\n8\n9\n10\n11\n14\n17\n18\n19\n20\n23\n24\n25\n" &
+  "28\n31\n32\n33\n34\n35\n38\n39\n42\n45\n46\n47\n48\n49").newStringStream().part2()
+
+doAssert 8 == t2
+doAssert 19208 == t
diff --git a/2020/src/day9.nim b/2020/src/day9.nim
index d910651..ecb80b6 100644
--- a/2020/src/day9.nim
+++ b/2020/src/day9.nim
@@ -1,4 +1,4 @@
-import streams, sequtils, sets, options, deques, input_helpers, day1
+import streams, sequtils, options, deques, input_helpers, day1
 
 const WINDOW = 25