From f755290feb0227dbc76c60becd3f8d746d64af52 Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tk@the-tk.com>
Date: Sat, 11 Dec 2021 17:25:23 +0000
Subject: day 11: nim

---
 d11.nim | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 d11.nim

diff --git a/d11.nim b/d11.nim
new file mode 100644
index 0000000..73ddfe3
--- /dev/null
+++ b/d11.nim
@@ -0,0 +1,76 @@
+import std/os, std/sugar, std/strutils, std/sequtils
+
+type
+   OctoState = Natural
+   Map = tuple[map: seq[OctoState], width: int, height: int]
+
+proc read_map(filename: string): Map =
+   let f = open(filename)
+   defer: f.close()
+   result.map = collect:
+      for line in f.lines():
+         result.width = line.len
+         result.height += 1
+         for c in line:
+            (c.ord - '0'.ord).OctoState
+
+proc print_map(map: Map) =
+   for y in countup(0, map.height - 1):
+      for x in countup(0, map.width - 1):
+         stdout.write(('0'.ord + map.map[x + map.width * y]).char)
+      stdout.write('\n')
+
+proc solve(map: Map): tuple[part1, part2: int] =
+   var
+      current = map.map
+      flashed = new_seq[bool](current.len)
+      flash = new_seq[bool](current.len)
+      flashes = 0
+   for step in 1..1000:
+      #print_map((current, map.width, map.height))
+      #echo ""
+      flashed.apply(proc(_: bool): bool = false)
+      current.apply(proc(s: OctoState): OctoState = s + 1)
+      while true:
+         var any = false
+         flash.apply(proc(_: bool): bool = false)
+         for i, s in current:
+            if flashed[i] or s <= 9: continue
+            flashed[i] = true
+            flash[i] = true
+            any = true
+         if not any: break
+         for i, s in flash:
+            if not s: continue
+            let
+               x = i mod map.width
+               y = i div map.width
+            for dy in countup(-1, 1):
+               for dx in countup(-1, 1):
+                  if dx == 0 and dy == 0: continue
+                  let
+                     x = x + dx
+                     y = y + dy
+                  if x < 0 or x >= map.width: continue
+                  if y < 0 or y >= map.height: continue
+                  inc current[x + map.width * y]
+      var sum = 0
+      for i, s in flashed:
+         if not s: continue
+         current[i] = 0
+         inc sum
+      flashes += sum
+      if step == 100:
+         result.part1 = flashes
+      if sum == map.width * map.height:
+         result.part2 = step
+         break
+
+when is_main_module:
+   var filename: string = "11.in"
+   if param_count() == 1:
+      filename = param_str(1)
+   let map = read_map(filename)
+   let (part1, part2) = solve(map)
+   echo part1
+   echo part2
-- 
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