diff --git a/mark/0_dayn/example.txt b/mark/0_dayn/example.txt
new file mode 100644
index 0000000..e69de29
diff --git a/mark/0_dayn/input.txt b/mark/0_dayn/input.txt
new file mode 100644
index 0000000..e69de29
diff --git a/mark/0_dayn/part1.rb b/mark/0_dayn/part1.rb
new file mode 100644
index 0000000..ff3a55e
--- /dev/null
+++ b/mark/0_dayn/part1.rb
@@ -0,0 +1,61 @@
+require 'debug'
+
+# Generic FileHandler
+class FileHandler
+  def initialize(file_path)
+    @file_path = file_path
+  end
+
+  # Usage:
+  # FileHandler.new('/path_to_file').read_lines do |line|
+  #   # process line
+  # end
+  def read_lines
+    File.foreach(@file_path, chomp: true).map do |line|
+      yield(line)
+    end
+  end
+
+  # Usage:
+  # file_content = FileHandler.new('/path_to_file').read_file(
+  def read_file
+    File.read(@file_path)
+  end
+end
+
+class PuzzleSolver
+  def initialize(file_handler, debug: false)
+    @handler = file_handler
+    @debug = debug
+  end
+
+  def debug(message)
+    puts message if @debug
+  end
+
+  def print_debug(message)
+    print message if @debug
+  end
+
+  def solve
+    raise NotImplementedError, 'Please implement this method in subclasses.'
+  end
+end
+
+# TODO: Puzzle-specific
+
+
+
+if ARGV[0].nil? || ARGV[0].empty?
+  puts "Usage: ruby #{__FILE__} <file_name> [debug]"
+  exit 1
+end
+file_path = ARGV[0]
+debug = (ARGV[1] == "debug")
+file_handler = FileHandler.new(file_path)
+
+## Puzzle-specific
+cls = PuzzleSolver
+##
+
+puts "The answer is: #{cls.new(file_handler, debug:).solve}"
diff --git a/mark/day5/example.txt b/mark/day5/example.txt
new file mode 100644
index 0000000..ca4fb6b
--- /dev/null
+++ b/mark/day5/example.txt
@@ -0,0 +1,11 @@
+3-5
+10-14
+16-20
+12-18
+
+1
+5
+8
+11
+17
+32
\ No newline at end of file
diff --git a/mark/day5/input.txt b/mark/day5/input.txt
new file mode 100644
index 0000000..dcbdb0f
--- /dev/null
+++ b/mark/day5/input.txt
@@ -0,0 +1,1175 @@
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\ No newline at end of file
diff --git a/mark/day5/part1.rb b/mark/day5/part1.rb
new file mode 100644
index 0000000..87b8b10
--- /dev/null
+++ b/mark/day5/part1.rb
@@ -0,0 +1,102 @@
+require 'debug'
+
+# Generic FileHandler
+class FileHandler
+  def initialize(file_path)
+    @file_path = file_path
+  end
+
+  # Usage:
+  # FileHandler.new('/path_to_file').read_lines do |line|
+  #   # process line
+  # end
+  def read_lines
+    File.foreach(@file_path, chomp: true).map do |line|
+      yield(line)
+    end
+  end
+
+  # Usage:
+  # file_content = FileHandler.new('/path_to_file').read_file(
+  def read_file
+    File.read(@file_path, chomp: true)
+  end
+end
+
+class PuzzleSolver
+  def initialize(file_handler, debug: false)
+    @handler = file_handler
+    @debug = debug
+  end
+
+  def debug(message)
+    puts message if @debug
+  end
+
+  def print_debug(message)
+    print message if @debug
+  end
+
+  def solve
+    raise NotImplementedError, 'Please implement this method in subclasses.'
+  end
+end
+
+class FreshnessDatabase
+  # @param [<Range>] list of ranges of fresh IDs
+  def initialize(fresh_ranges)
+    @fresh_ranges = fresh_ranges
+  end
+
+  def fresh_id?(id)
+    @fresh_ranges.any? {|range| range.include?(id)}
+  end
+end
+
+class Solver < PuzzleSolver
+  # @param [String] e.g., "11-22"
+  # @return [Range] e.g., 11..22 (inclusive)
+  def to_range(string)
+    boundaries = string.split('-').map(&:to_i)
+    raise "Invalid boundaries for #{string}, got #{boundaries.inspect}" if boundaries.length != 2
+    Range.new(boundaries[0], boundaries[1])
+  end
+
+  # @param [String] full input e.g., "11-22\n33-604\n..."
+  # @return [<Range>] e.g., [11..22, 33..604, ...]
+  def parse_ranges(input)
+    input.split("\n").map {|range| to_range(range)}
+  end
+
+  # @param [String] ids_str e.g., "1\n5\n8\n11\n17\n32"
+  # @return [<Integer>] e.g., [1, 5, 8, 11, 17, 32]
+  def parse_ids(ids_str)
+    ids_str.split("\n").map(&:to_i)
+  end
+
+  def solve
+    two_parts = @handler.read_file.split("\n\n")
+    raise "Invalid file format: #{two_parts.inpsect}" if two_parts.length != 2
+
+    db = FreshnessDatabase.new(parse_ranges(two_parts[0]))
+    ids = parse_ids(two_parts[1])
+
+    fresh_ids = ids.select {|id| db.fresh_id?(id)}
+    fresh_ids.length
+  end
+end
+
+
+if ARGV[0].nil? || ARGV[0].empty?
+  puts "Usage: ruby #{__FILE__} <file_name> [debug]"
+  exit 1
+end
+file_path = ARGV[0]
+debug = (ARGV[1] == "debug")
+file_handler = FileHandler.new(file_path)
+
+## Puzzle-specific
+cls = Solver
+##
+
+puts "The answer is: #{cls.new(file_handler, debug:).solve}"
diff --git a/mark/day5/part2.rb b/mark/day5/part2.rb
new file mode 100644
index 0000000..b006202
--- /dev/null
+++ b/mark/day5/part2.rb
@@ -0,0 +1,198 @@
+require 'debug'
+
+# Generic FileHandler
+class FileHandler
+  def initialize(file_path)
+    @file_path = file_path
+  end
+
+  # Usage:
+  # FileHandler.new('/path_to_file').read_lines do |line|
+  #   # process line
+  # end
+  def read_lines
+    File.foreach(@file_path, chomp: true).map do |line|
+      yield(line)
+    end
+  end
+
+  # Usage:
+  # file_content = FileHandler.new('/path_to_file').read_file(
+  def read_file
+    File.read(@file_path, chomp: true)
+  end
+end
+
+class PuzzleSolver
+  def initialize(file_handler, debug: false)
+    @handler = file_handler
+    @debug = debug
+  end
+
+  def debug(message)
+    puts message if @debug
+  end
+
+  def print_debug(message)
+    print message if @debug
+  end
+
+  def solve
+    raise NotImplementedError, 'Please implement this method in subclasses.'
+  end
+end
+
+class FreshnessDatabase
+  # @param [<Range>] list of ranges of fresh IDs
+  def initialize(fresh_ranges)
+    @fresh_ranges = fresh_ranges
+  end
+
+  def fresh_id?(id)
+    @fresh_ranges.any? {|range| range.include?(id)}
+  end
+
+  def parsed_ranges
+    all_ranges = []
+    current_min = Float::INFINITY
+    current_max = -Float::INFINITY
+    @fresh_ranges.each_with_index do |range, index|
+      if range.max < current_min
+        all_ranges.insert(0, range)
+        current_min = range.min
+        current_max = range.max if range.max > current_max
+        next
+      end
+
+      if range.min > current_max
+        all_ranges << range
+        current_max = range.max
+        current_min = range.min if range.min < current_min
+        next
+      end
+
+      overlapping_range_indices, closest_range_index = FreshnessDatabase.find_all_overlapping_range_indices(all_ranges, range)
+
+      if overlapping_range_indices.empty?
+        all_ranges.insert(closest_range_index + 1, range)
+      elsif overlapping_range_indices.length == 1
+        overlap_index = overlapping_range_indices[0]
+        new_range = FreshnessDatabase.max_range([all_ranges[overlap_index], range])
+        all_ranges[overlap_index] = new_range
+        range = new_range
+      else
+        min_index = overlapping_range_indices[0]
+        max_index = overlapping_range_indices[overlapping_range_indices.length - 1]
+        min_range = all_ranges[min_index]
+        max_range = all_ranges[max_index]
+        new_range = FreshnessDatabase.max_range([min_range, range, max_range])
+
+        new_ranges = []
+        all_ranges.each_index do |i|
+          if i < min_index
+            new_ranges << all_ranges[i]
+          elsif i == min_index
+            new_ranges << new_range
+          elsif min_index < i && i <= max_index
+            # do nothing
+          else
+            new_ranges << all_ranges[i]
+          end
+        end
+        all_ranges = new_ranges
+        range = new_range
+      end
+
+      current_min = range.min if range.min < current_min
+      current_max = range.max if range.max > current_max
+    end
+
+    all_ranges
+  end
+
+  def num_fresh_ids
+    ranges = parsed_ranges
+    puts ranges.inspect
+    num_ids = ranges.map {|range| range.size}.sum
+
+    num_ids
+  end
+
+  private
+
+  def self.overlapping_ranges?(range1, range2)
+    (range1.min <= range2.min && range2.min <= range1.max) ||
+    (range1.min <= range2.max && range2.min <= range1.max)
+  end
+
+  def self.max_range(ranges_array)
+    (0...ranges_array.length - 1).each do |index|
+      raise "Non overlapping ranges found on #{index}: #{ranges_array}" if !self.overlapping_ranges?(ranges_array[index], ranges_array[index+1])
+    end
+
+    bounds = ranges_array.flat_map {|range| [range.min, range.max]}
+    Range.new(bounds.min, bounds.max)
+  end
+
+  def self.find_all_overlapping_range_indices(all_ranges, range)
+    # NOTE: we assume `range` is between smallest and largest range, as those cases are handles separately in main loop
+    raise "Error unmet assumption: #{all_ranges}" if all_ranges.length < 2
+
+    indices = []
+    closest_range_index = 0 # used in case there is no overlap
+    all_ranges.each_with_index do |possible_range, index|
+      if self.overlapping_ranges?(possible_range, range)
+        indices << index
+      else
+        closest_range_index = index if range.min > possible_range.max
+      end
+    end
+
+    [indices, closest_range_index]
+  end
+end
+
+class Solver < PuzzleSolver
+  # @param [String] e.g., "11-22"
+  # @return [Range] e.g., 11..22 (inclusive)
+  def to_range(string)
+    boundaries = string.split('-').map(&:to_i)
+    raise "Invalid boundaries for #{string}, got #{boundaries.inspect}" if boundaries.length != 2
+    Range.new(boundaries[0], boundaries[1])
+  end
+
+  # @param [String] full input e.g., "11-22\n33-604\n..."
+  # @return [<Range>] e.g., [11..22, 33..604, ...]
+  def parse_ranges(input)
+    input.split("\n").map {|range| to_range(range)}
+  end
+
+  # @param [String] ids_str e.g., "1\n5\n8\n11\n17\n32"
+  # @return [<Integer>] e.g., [1, 5, 8, 11, 17, 32]
+  def parse_ids(ids_str)
+    ids_str.split("\n").map(&:to_i)
+  end
+
+  def solve
+    two_parts = @handler.read_file.split("\n\n")
+    raise "Invalid file format: #{two_parts.inpsect}" if two_parts.length != 2
+
+    db = FreshnessDatabase.new(parse_ranges(two_parts[0]))
+    db.num_fresh_ids
+  end
+end
+
+
+if ARGV[0].nil? || ARGV[0].empty?
+  puts "Usage: ruby #{__FILE__} <file_name> [debug]"
+  exit 1
+end
+file_path = ARGV[0]
+debug = (ARGV[1] == "debug")
+file_handler = FileHandler.new(file_path)
+
+## Puzzle-specific
+cls = Solver
+##
+
+puts "The answer is: #{cls.new(file_handler, debug:).solve}"