day 5, part 2

implentation copied from Brandon Mitchell and then reworked into my map chain shenanigans

Author: Robb Kidd

2023/ruby/day05.rb

@@ -19,8 +19,34 @@ def part1
   end
 
   # @example
-  #   day.part2 #=> 'how are you'
+  #   day.part2 #=> 46
   def part2
+    maps = parse
+
+    maps["seeds"]
+      .each_slice(2)
+      .map { |start, length|
+        min = Float::INFINITY
+        i = 0
+        while i < length do
+          location, skip =
+            [start + i]
+              .map{ maps["seed-to-soil"]           .convert_with_skip(_1)  } # no skip to start
+              .map{ maps["soil-to-fertilizer"]     .convert_with_skip(*_1) } # <- from here on _1
+              .map{ maps["fertilizer-to-water"]    .convert_with_skip(*_1) } # is [previous_conversion, skip]
+              .map{ maps["water-to-light"]         .convert_with_skip(*_1) }
+              .map{ maps["light-to-temperature"]   .convert_with_skip(*_1) }
+              .map{ maps["temperature-to-humidity"].convert_with_skip(*_1) }
+              .map{ maps["humidity-to-location"]   .convert_with_skip(*_1) }
+              .first
+
+          min = location if location < min
+          i = i + skip if 0 < skip
+          i = i + 1
+        end
+        min
+      }
+      .min
   end
 
   def parse
@@ -42,9 +68,7 @@ def parse
     maps
   end
 
-  # @example
-  #   mapper = Day05::Mapper.new(["50 98 2", "52 50 48"])
-  #   mapper.convert(79) #=> 81
+
   class Mapper
     attr_reader :map_title, :maps
 
@@ -57,6 +81,9 @@ def initialize(map_title, maps)
                 }
     end
 
+    # @example
+    #   mapper = Day05::Mapper.new("test", ["50 98 2", "52 50 48"])
+    #   mapper.convert(79) #=> 81
     def convert(input)
       maps.each do |source_range, dest_start|
         next unless source_range.cover?(input)
@@ -65,6 +92,45 @@ def convert(input)
 
       return input
     end
+
+    # @example seed-to-soil
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["seed-to-soil"].convert_with_skip(82) #=> [84, 15]
+    # @example soil-to-fertilizer
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["soil-to-fertilizer"].convert_with_skip(84, 15) #=> [84, 15]
+    # @example fertilizer-to-water
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["fertilizer-to-water"].convert_with_skip(84, 15) #=> [84, 15]
+    # @example water-to-light
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["water-to-light"].convert_with_skip(84, 15) #=> [77, 10]
+    # @example light-to-temperature
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["light-to-temperature"].convert_with_skip(77, 10) #=> [45, 10]
+    # @example temperature-to-humidity
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["temperature-to-humidity"].convert_with_skip(45, 10) #=> [46, 10]
+    # @example humidity-to-location
+    #  maps = Day05.new(Day05::EXAMPLE_INPUT).parse
+    #  maps["humidity-to-location"].convert_with_skip(46, 10) #=> [46, 9]
+    #
+    # logic copied enthusiastically from Brandon Mitchell; I couldn't figure it out
+    def convert_with_skip(input, skip=-1)
+      maps.each do |source_range, dest_start|
+        if source_range.cover?(input)
+          if skip && skip > source_range.size - (input - source_range.min) - 1
+            skip = source_range.size - (input - source_range.min) - 1
+          end
+          return [dest_start + (input - source_range.min), skip]
+        end
+        if input < source_range.min && (skip < 0 || skip > source_range.min - input -1)
+          skip = source_range.min - input - 1
+        end
+      end
+
+      return [input, skip]
+    end
   end
 
   EXAMPLE_INPUT = <<~INPUT