From 2df9608c6af99f5550f9c9569b5fe2630d8ec4a5 Mon Sep 17 00:00:00 2001
From: Shanti Chellaram <shanti@shanti.im>
Date: Mon, 19 Dec 2022 16:28:51 +0900
Subject: [PATCH] Day 14-2

---
 day14.erl | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/day14.erl b/day14.erl
index 9b39f4a..9a2a760 100644
--- a/day14.erl
+++ b/day14.erl
@@ -3,11 +3,25 @@
 -export([solve/1]).
 
 solve(Input) ->
-    {part1(Input), none}.
+    {part1(Input), part2(Input)}.
 
 
 part1(Input) -> simulate(parse_map(Input), 0).
 
+part2(Input) ->
+    simulate(parse_map2(Input), 0).
+
+parse_map2(Input) ->
+    LineSegments = parse_instructions(Input),
+    FloorDepth = y_max(LineSegments, 0) + 2,
+    FlooredLineSegments = [{{500 - FloorDepth, FloorDepth}, {500 + FloorDepth, FloorDepth}} | LineSegments],
+    ChoppedSegments = chop_segments(FlooredLineSegments, []),
+    SegmentMap = maps:groups_from_list(fun({X, _, _}) -> X end, fun({_X, YStart, YEnd}) -> {YStart, YEnd} end, ChoppedSegments),
+    maps:map(fun (_Key, Segments) -> lists:foldl(fun rset_append/2, rset_new(), Segments) end, SegmentMap).
+
+y_max([], Max) -> Max;
+y_max([{{_, Y1},{_,Y2}}|Rest], Max) -> y_max(Rest, max(max(Y1, Y2), Max)).
+
 parse_map(Input) ->
     LineSegments = parse_instructions(Input),
     ChoppedSegments = chop_segments(LineSegments, []),
@@ -45,6 +59,7 @@ chop_segments([{{X1, Y}, {X2, Y}} | Rest], Acc) -> chop_segments(Rest, [{X, Y, Y
 
 simulate(State, SandCount) ->
     case attempt_place(State, {500, 0}) of
+        {500, 0} -> SandCount + 1;
         {X, Y} -> simulate(State#{X := rset_append({Y, Y}, maps:get(X, State))}, SandCount+1);
         falling -> SandCount
     end.
@@ -83,15 +98,7 @@ rset_append({_, End} = Entry, [{HeadStart, _} | _] = Set) when End < HeadStart -
 rset_append({Start, _} = Entry, [{_, HeadEnd} = Head | Rest]) when Start > HeadEnd + 1 -> [ Head | rset_append(Entry, Rest)];
 rset_append({Start, End}, [{HeadStart, HeadEnd} | Rest]) -> rset_append({min(Start, HeadStart), max(End, HeadEnd)}, Rest).
 
-rset_contains(Item, []) -> false;
-rset_contains(Item, [{Start, _}|Rest]) when Item < Start -> false;
+rset_contains(_Item, []) -> false;
+rset_contains(Item, [{Start, _}|_Rest]) when Item < Start -> false;
 rset_contains(Item, [{_, End}|Rest]) when Item > End -> rset_contains(Item, Rest);
 rset_contains(_Item, _Rest) -> true.
-
-rset_remove1(_Point, []) -> [];
-rset_remove1(Point, [{Start, _End} | _Rest] = Set) when Point < Start -> Set;
-rset_remove1(Point, [{_Start, End} = Head | Rest]) when Point > End -> [Head | rset_remove1(Point, Rest)];
-rset_remove1(Point, [{Point, Point} | Rest]) -> Rest;
-rset_remove1(Point, [{Point, End} | Rest]) -> [{Point+1, End} | Rest];
-rset_remove1(Point, [{Start, Point} | Rest]) -> [{Start, Point-1} | Rest];
-rset_remove1(Point, [{Start, End} | Rest]) -> [{Start, Point-1}, {Point+1, End} | Rest].