Add solution for 2015 day 03

2015/README.md

@@ -3,7 +3,7 @@
 ## Progress
 - [x] Day 01
 - [x] Day 02
-- [ ] Day 03
+- [x] Day 03
 - [ ] Day 04
 - [ ] Day 05
 - [ ] Day 06

2015/day-03/inputs/test.txt

@@ -0,0 +1,6 @@
+>
+^>v<
+^v^v^v^v^v
+^v
+^>v<
+^v^v^v^v^v

2015/day-03/main.rb

@@ -0,0 +1,78 @@
+#!/usr/bin/env ruby
+
+require "pathname"
+require "set"
+
+INPUTS = [
+  Pathname("inputs/test.txt"),
+  Pathname("inputs/puzzle.txt"),
+].freeze
+
+def position_modifier(direction)
+  case direction
+  when ">" then [1, 0]
+  when "<" then [-1, 0]
+  when "^" then [0, 1]
+  when "v" then [0, -1]
+  end
+end
+
+def apply_direction(position, change)
+  position.map.with_index { |v, i| v + change[i] }
+end
+
+def next_position(position, direction)
+  apply_direction(position, position_modifier(direction))
+end
+
+def solve_part_1(input)
+  input.lines.map do |line|
+    puts "  " + "-" * 10
+
+    position = [0, 0]
+
+    houses =
+      line.chomp.each_char.each_with_object(Set[position]) do |direction, visited|
+        next_pos = next_position(position, direction)
+        visited.add(next_pos)
+        position = next_pos
+      end
+
+    puts "  Houses: #{houses.size}"
+  end
+end
+
+def solve_part_2(input)
+  input.lines.map do |line|
+    puts "  " + "-" * 10
+
+    position_s = [0, 0]
+    position_r = position_s.dup
+
+    houses =
+      line.chomp.each_char.each_with_object(Set[position_s.dup]).with_index(1) do |(direction, visited), index|
+        if index.even?
+          next_pos = next_position(position_s, direction)
+          visited.add(next_pos)
+          position_s = next_pos
+        else
+          next_pos = next_position(position_r, direction)
+          visited.add(next_pos)
+          position_r = next_pos
+        end
+      end
+
+    puts "  Houses: #{houses.size}"
+  end
+end
+
+def main(files)
+  files.each do |file|
+    puts "File: #{file}"
+    solve_part_1(file.read.chomp)
+    puts "=" * 15
+    solve_part_2(file.read.chomp)
+  end
+end
+
+main(INPUTS)