From c45d2e403278608e4c0baef70343e03149d499b3 Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tk@the-tk.com>
Date: Mon, 6 Dec 2021 23:04:43 +0000
Subject: day 5: nim

---
 d5.nim | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 d5.nim

diff --git a/d5.nim b/d5.nim
new file mode 100644
index 0000000..5c5e94e
--- /dev/null
+++ b/d5.nim
@@ -0,0 +1,71 @@
+import std/sets, std/strutils, std/sugar, std/sequtils, std/os
+
+type
+   Num = range[0..9999999]
+   Pos = tuple[x, y: Num]
+   Vent = tuple[a, b: Pos]
+   VentType = enum vt_horz vt_vert vt_diag
+
+proc parse_pos(pos: string): Pos =
+   let xy = pos.split(',', maxsplit=1).map(parse_int)
+   return (xy[0].Num, xy[1].Num)
+
+proc read_vents(filename: string): seq[Vent] =
+   let f = open(filename)
+   defer: f.close()
+   result = collect:
+      for line in f.lines():
+         let ab = line.split(" -> ", maxsplit=1).map(parse_pos)
+         (ab[0], ab[1])
+
+func classify(v: Vent): VentType =
+   if v.a.x == v.b.x:
+      return vt_vert
+   if v.a.y == v.b.y:
+      return vt_horz
+   return vt_diag
+
+iterator intersect(u, v: Vent): Pos =
+   var
+      uc = classify(u)
+      vc = classify(v)
+   if uc == vc:
+      for x in max(u.a.x, v.a.x) .. min(u.b.x, v.b.x):
+         for y in max(u.a.y, v.a.y) .. min(u.b.y, v.b.y):
+            yield (x, y)
+   else:
+      var
+         u = u
+         v = v
+      if uc == vt_vert and vc == vt_horz:
+         (u, v) = (v, u)
+      let
+         x = v.a.x
+         y = u.a.y
+      if x >= u.a.x and x <= u.b.x and y >= v.a.y and y <= v.b.y:
+         yield (x, y)
+
+func normalise(v: Vent): Vent =
+   result = v
+   if ((classify(v) != vt_vert and v.b.x < v.a.x) or
+       (classify(v) == vt_vert and v.b.y < v.a.y)):
+      result = (v.b, v.a)
+
+proc part1(vents: seq[Vent]): int =
+   var intersections: HashSet[Pos]
+   for i, a in vents:
+      if classify(a) == vt_diag: continue
+      let a = normalise(a)
+      for b in vents[i + 1 .. ^1]:
+         if classify(b) == vt_diag: continue
+         let b = normalise(b)
+         for p in intersect(a, b):
+            intersections.incl(p)
+   return len(intersections)
+
+when is_main_module:
+   var filename: string = "5.in"
+   if param_count() == 1:
+      filename = param_str(1)
+   let vents = read_vents(filename)
+   echo part1(vents)
-- 
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