add day_07

day_07/1.rb

@@ -0,0 +1,42 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require_relative "graph"
+
+class Main
+  def run
+    input = $stdin.readlines.map(&:chomp)
+    graph = Graph.new(input)
+
+    total = dfs(graph.start, graph, 0, Set.new)
+    puts total
+  end
+
+  def dfs(next_point, graph, total, visited)
+    if next_point.y > graph.height || visited.include?(next_point)
+      return total
+    end
+
+    if graph.at(next_point) == "^"
+      step_west = Point.new(next_point.x - 1, next_point.y)
+      step_east = Point.new(next_point.x + 1, next_point.y)
+
+      if graph.at(step_west) == "." ||
+          graph.at(step_east) == "."
+        total += 1
+      end
+
+      # step west then dfs south
+      total = dfs(step_west, graph, total, visited) # west
+      # step east then dfs south
+      total = dfs(step_east, graph, total, visited) # east
+      return total
+    elsif graph.at(next_point) == "."
+      visited.add(next_point)
+    end
+
+    dfs(Point.new(next_point.x, next_point.y + 1), graph, total, visited) # south
+  end
+end
+
+Main.new.run

day_07/2.rb

@@ -0,0 +1,41 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require_relative "graph"
+
+class Main
+  def run
+    lines = $stdin.readlines(chomp: true)
+    graph = Graph.new(lines)
+    counts = Hash.new(0)
+    counts[graph.start.x] = 1
+
+    process_graph(lines, graph, counts)
+    puts counts.values.sum
+  end
+
+  def process_graph(lines, graph, counts)
+    lines.each_with_index do |line, y|
+      line.chars.each_with_index do |char, x|
+        current = Point.new(x, y)
+
+        next unless graph.at(current) == "^"
+
+        distribute_counts(x, y, counts)
+      end
+    end
+  end
+
+  # When we encounter a "^", we split the count to the west and east positions
+  # and reset the current position count to 0.
+  def distribute_counts(x, y, counts)
+    peek_west = Point.new(x - 1, y)
+    peek_east = Point.new(x + 1, y)
+
+    counts[peek_west.x] += counts[x]
+    counts[peek_east.x] += counts[x]
+    counts[x] = 0
+  end
+end
+
+Main.new.run

day_07/graph.rb

@@ -0,0 +1,32 @@
+require "forwardable"
+
+require_relative "point"
+
+class Graph
+  attr_reader :start, :height, :width
+  extend Forwardable
+  def_delegators :@data, :[]
+
+  def initialize(input)
+    @data = input.each_with_index.map do |line, y|
+      if y.zero?
+        @start = Point.new(line.index("S"), y)
+      end
+      line.chars
+    end
+    @width = @data[0].size - 1
+    @height = @data.size - 1
+  end
+
+  def to_s
+    @data.map { |row| row.join("") }.join("\n")
+  end
+
+  def at(point)
+    @data[point.y][point.x]
+  end
+
+  def out_of_bounds?(point)
+    point.x < 0 || point.x > @width || point.y < 0 || point.y > @height
+  end
+end

day_07/point.rb

@@ -0,0 +1,24 @@
+class Point
+  attr_reader :x, :y
+
+  def initialize(x, y)
+    @x = x
+    @y = y
+  end
+
+  def to_s
+    "(#{x}, #{y})"
+  end
+
+  def ==(other)
+    x == other.x && y == other.y
+  end
+
+  def hash
+    [x, y].hash
+  end
+
+  def eql?(other)
+    self == other
+  end
+end