Add day13 problem description

day13/p1.nim

@@ -0,0 +1,42 @@
+import os, sets
+import std/[strutils, sequtils]
+
+type
+  Dot = (uint16, uint16)
+
+proc main() =
+  let fileName = paramStr(1)
+
+  var dots = HashSet[Dot]()
+
+  for line in fileName.lines:
+    if line.strip() == "":
+      continue
+
+    if not line.startsWith("fold"):
+      let split = line.strip.split(",")
+      dots.incl (split[0].parseInt.uint16, split[1].parseInt.uint16)
+    else:
+      var fold: (int, int) = (-1, -1)
+
+      if line.startsWith("fold along x="):
+        fold[0] = line.replace("fold along x=", "").parseInt
+      else:
+        fold[1] = line.replace("fold along y=", "").parseInt
+
+      for dot in dots.deepCopy:
+        var newDot: Dot = dot
+        if fold[0] != -1 and dot[0] > fold[0].uint16:
+          newDot[0] = 2*fold[0].uint16 - dot[0]
+          dots.excl dot
+        if fold[1] != -1 and dot[1] > fold[1].uint16:
+          newDot[1] = 2*fold[1].uint16 - dot[1]
+          dots.excl dot
+
+        dots.incl newDot
+
+      echo "Number of dots after one fold: ", dots.len
+      return
+
+
+main()