Day 9: Explosives in Cyberspace (1st & 2nd)

Author: rab

README.md

@@ -13,6 +13,7 @@ My Personal [Leaderboard] stats:
 <pre>
       --Part 1---   --Part 2---
 Day   Rank  Score   Rank  Score
+  9    387      0    193      0  A couple of off-by-one errors slowed me down
   8   2224      0   2177      0
   7    210      0    330      0  This one really gave me trouble. 3rd answer for * and 2nd for **
   6    294      0    271      0

day09.rb

@@ -0,0 +1,145 @@
+# --- Day 9: Explosives in Cyberspace ---
+#
+# Wandering around a secure area, you come across a datalink port to a new part of the
+# network. After briefly scanning it for interesting files, you find one file in particular that
+# catches your attention. It's compressed with an experimental format, but fortunately, the
+# documentation for the format is nearby.
+#
+# The format compresses a sequence of characters. Whitespace is ignored. To indicate that some
+# sequence should be repeated, a marker is added to the file, like (10x2). To decompress this
+# marker, take the subsequent 10 characters and repeat them 2 times. Then, continue reading the
+# file after the repeated data.  The marker itself is not included in the decompressed output.
+#
+# If parentheses or other characters appear within the data referenced by a marker, that's okay -
+# treat it like normal data, not a marker, and then resume looking for markers after the
+# decompressed section.
+#
+# For example:
+#
+#
+# ADVENT contains no markers and decompresses to itself with no changes, resulting in a
+# decompressed length of 6.
+#
+# A(1x5)BC repeats only the B a total of 5 times, becoming ABBBBBC for a decompressed length of 7.
+#
+# (3x3)XYZ becomes XYZXYZXYZ for a decompressed length of 9.
+#
+# A(2x2)BCD(2x2)EFG doubles the BC and EF, becoming ABCBCDEFEFG for a decompressed length of 11.
+#
+# (6x1)(1x3)A simply becomes (1x3)A - the (1x3) looks like a marker, but because it's within a
+# data section of another marker, it not treated any differently from the A that comes after
+# it. It has a decompressed length of 6.
+#
+# X(8x2)(3x3)ABCY becomes X(3x3)ABC(3x3)ABCY (for a decompressed length of 18), because the
+# decompressed data from the (8x2) marker (the (3x3)ABC) is skipped and not processed further.
+#
+# What is the decompressed length of the file (your puzzle input)? Don't count whitespace.
+#
+# --- Part Two ---
+#
+# Apparently, the file actually uses version two of the format.
+#
+# In version two, the only difference is that markers within decompressed data are
+# decompressed. This, the documentation explains, provides much more substantial compression
+# capabilities, allowing many-gigabyte files to be stored in only a few kilobytes.
+#
+# For example:
+#
+# (3x3)XYZ still becomes XYZXYZXYZ, as the decompressed section contains no markers.
+#
+# X(8x2)(3x3)ABCY becomes XABCABCABCABCABCABCY, because the decompressed data from the (8x2)
+# marker is then further decompressed, thus triggering the (3x3) marker twice for a total of six
+# ABC sequences.
+#
+# (27x12)(20x12)(13x14)(7x10)(1x12)A decompresses into a string of A repeated 241920 times.
+#
+# (25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN becomes 445 characters long.
+#
+# Unfortunately, the computer you brought probably doesn't have enough memory to actually
+# decompress the file; you'll have to come up with another way to get its decompressed length.
+#
+# What is the decompressed length of the file using this improved format?
+
+require_relative 'input'
+
+day = __FILE__[/\d+/].to_i(10)
+input = Input.for_day(day)
+
+# puts "solving day #{day} from input\n#{input.inspect}"
+
+def decompressed_size(string)
+  inpos = 0
+  limit = string.size
+  size = 0
+
+  marker = /\((\d+)x(\d+)\)/
+
+  piece = ''
+  while inpos < limit
+    if (char = string[inpos]) == '('        # marker?
+      until char == ')'
+        piece << char
+        inpos += 1
+        char = string[inpos]
+      end
+      piece << char
+      len, rep = marker.match(piece).captures.map(&:to_i)
+      inpos += len
+      piece = ''
+      size += len * rep
+    else
+      size += 1 unless /\s/.match char
+    end
+    inpos += 1
+  end
+
+  size
+end
+
+# puts "#{decompressed_size('ADVENT')} should be 6"
+# puts "#{decompressed_size('A(1x5)BC')} should be 7"
+# puts "#{decompressed_size('(3x3)XYZ')} should be 9"
+# puts "#{decompressed_size('A(2x2)BCD(2x2)EFG')} should be 11"
+# puts "#{decompressed_size('(6x1)(1x3)A')} should be 6"
+# puts "#{decompressed_size('X(8x2)(3x3)ABCY')} should be 18"
+
+puts "V1: #{decompressed_size(input)}"
+
+# --------------------------------------------------------------------------------
+def decompressed_size_v2(string)
+  inpos = 0
+  limit = string.size
+  size = 0
+
+  marker = /\((\d+)x(\d+)\)/
+
+  piece = ''
+  while inpos < limit
+    if (char = string[inpos]) == '('        # marker?
+      until char == ')'
+        piece << char
+        inpos += 1
+        char = string[inpos]
+      end
+      piece << char
+      len, rep = marker.match(piece).captures.map(&:to_i)
+      inpos += 1
+      delta = decompressed_size_v2(string[inpos,len])
+      inpos += len
+      size += delta * rep
+      piece = ''
+    else
+      inpos += 1
+      size += 1 unless /\s/.match char
+    end
+  end
+
+  size
+end
+
+# puts "#{decompressed_size_v2('(3x3)XYZ')} should be 9"
+# puts "#{decompressed_size_v2('X(8x2)(3x3)ABCY')} should be #{'XABCABCABCABCABCABCY'.length}"
+# puts "#{decompressed_size_v2('(27x12)(20x12)(13x14)(7x10)(1x12)A')} should be 241920"
+# puts "#{decompressed_size_v2('(25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN')} should be 445"
+
+puts "V2: #{decompressed_size_v2(input)}"