advent of code - day 3

day03.rb

def current_position(previous, move)
  x, y = 0, 0
  case move
  when '^' then y += 1
  when '>' then x += 1
  when 'v' then y -= 1
  when '<' then x -= 1
  end
  [ previous[0] + x, previous[1] + y ]
end

def map_deliveries(directions)
  deliveries = [ [0, 0] ]
  directions.each do |move|
    previous = deliveries.last
    deliveries.push current_position(previous, move)
  end
  deliveries
end

def solo_santa_deliveries
  map_deliveries(@input.chars)
end

def santa_deliveries
  directions = @input.chars.select.with_index { |x, i| i.even? }
  map_deliveries(directions)
end

def robo_santa_deliveries
  directions = @input.chars.select.with_index { |x, i| i.odd? }
  map_deliveries(directions)
end

def calculate_houses
  results = {
    solo: solo_santa_deliveries.uniq.length,
    helper: (santa_deliveries + robo_santa_deliveries).uniq.length
  }
end

@input = File.read('input').strip

puts "Houses that received at least one gift from Santa: #{calculate_houses[:solo]}"
puts "Houses that received at least one gift from Santa or Robo-Santa: #{calculate_houses[:helper]}"

day3a.md

Day 3: Perfectly Spherical Houses in a Vacuum

Santa is delivering presents to an infinite two-dimensional grid of houses.

He begins by delivering a present to the house at his starting location, and then an elf at the North Pole calls him via radio and tells him where to move next. Moves are always exactly one house to the north (^), south (v), east (>), or west (<). After each move, he delivers another present to the house at his new location.

However, the elf back at the north pole has had a little too much eggnog, and so his directions are a little off, and Santa ends up visiting some houses more than once. How many houses receive at least one present?

For example:

• > delivers presents to 2 houses: one at the starting location, and one to the east.
• ^>v< delivers presents to 4 houses in a square, including twice to the house at his starting/ending location.
• ^v^v^v^v^v delivers a bunch of presents to some very lucky children at only 2 houses.

day3a.rb

x, y = 0, 0
moves = [ [x, y] ]
input = File.read('input')

input.chars.each do |move|
  case move
  when '^' then y += 1
  when '>' then x += 1
  when 'v' then y -= 1
  when '<' then x -= 1
  end
  moves.push [x, y]
end

houses = moves.uniq.size

puts "Houses that receive at least one present: #{houses}"

day3b.md

Part Two

The next year, to speed up the process, Santa creates a robot version of himself, Robo-Santa, to deliver presents with him.

Santa and Robo-Santa start at the same location (delivering two presents to the same starting house), then take turns moving based on instructions from the elf, who is eggnoggedly reading from the same script as the previous year.

This year, how many houses receive at least one present?

For example:

• ^v delivers presents to 3 houses, because Santa goes north, and then Robo-Santa goes south.
• ^>v< now delivers presents to 3 houses, and Santa and Robo-Santa end up back where they started.
• ^v^v^v^v^v now delivers presents to 11 houses, with Santa going one direction and Robo-Santa going the other.

day3b.rb

def directions(santa)
  input = File.read('input').strip
  input.chars.select.with_index { |x, i| i.send(santa) }
end

def current_position(previous, move)
  x, y = 0, 0
  case move
  when '^' then y += 1
  when '>' then x += 1
  when 'v' then y -= 1
  when '<' then x -= 1
  end
  [ previous[0] + x, previous[1] + y ]
end

def map_deliveries(santa)
  deliveries = [ [0, 0] ]
  directions(santa).each do |move|
    previous = deliveries.last
    deliveries.push current_position(previous, move)
  end
  deliveries
end

def santa_deliveries
  map_deliveries(:even?)
end

def robo_santa_deliveries
  map_deliveries(:odd?)
end

def calculate_houses
  (santa_deliveries + robo_santa_deliveries).uniq.length
end

puts "Santa delivered to #{santa_deliveries.length} houses"
puts "Robo Santa delivered to #{robo_santa_deliveries.length} houses"
puts "Houses that receive at least one present: #{calculate_houses}"

input

v>v<vvv<<vv^v<v>vv>v<<<^^^^^<<^<vv>^>v^>^>^>^>^><vvvv<^>^<<^><<<^vvvv>^>^><^v^><^<>^^>^vvv^<vv>>^>^^<>><>^>vvv>>^vv>^<><>^<v^>^>^><vv^vv^>><<^><<v>><>^<^>>vvv>v>>>v<<^<><^<v<>v>^^v^^^<^v^^>>><^>^>v<>^<>>^>^^v^><v<v>>><>v<v^v>^v<>>^><v>^<>v^>^<>^v^^^v^^>>vv<<^^><^<vvv>^>^^<^>>^^^^^v^<v>vv<>>v^v<^v^^<><^<^vv^><>><><>v>vvv^vv^^<<><<vvv><<^v^><v<>vvv^<^>vvvv^>^>>^v^<v^vv<^^v<>v>vv^<>><v<<<^v^<<><v<^<^<><^^^>^>>v>^>v^<>v><^<^<v^>^^vv<^^<>v^v^vv<>>>>v^v<>><^^v>vv^^>v^v>v<vv>>v>><v^v^v>vv>^^>^v><<vv^v^^vv<^v><^<<v<v^>vv^^^<v^>v>v^^^>><^^<v^<^>>v><vv<v^^>^^v>>v^^^<^^v>^v>><^<^<>>v<<^^vv>^^^v<^<^<v<v^^vv>^vv^>>v^><v>><<<>^vv^<^<>v^^<<<v<^>^><><v^^>>^^^<^vv<^^^>><^^v>^^v^<v^v^>^^<v>^<^v<^<<<<^<v^>v^<^^<>^^>^><<>>^v><>><^<v><^^^>>vv>^><vv>^^^^^v^vvv><><^<^>v>v^v^>^><><^<^><>v<<vv<^>><>^v^^v>^<<<>^v^>^<<v^vv<>v^<v^^vv><<v^<>>>^<v>vv>v>>>^<^>><vv<>>>>v<v>>>^v>v><>>vvv<^^><<^>^>v<^vvvv<v><vv<><^^^v^^^>v^v<>v<^^v>>><>v<v^>>v><v^>>^^<v<<<^<v<><^^v><<v^><<<<^vv<^<>^><vv<<<<^>>>^v>^v>vv>^v<>v>v<v><^>>v>>^>^><^<v^v^>^v<><><^^>^<vvvv^^<>^^^>vv^v^v>^v^^v^^v><v^<^<>><^<v>v>>vv<<v>>vvvv<vv><>>^v^>^>>v^v^<<<vv<><v<<>>>^v<<v>^^vv^><>v>^>v><<<<<<<^>^^v^<<^^>>vvv^<><>><>^^v<<vv><^^v<^^><vv>v^>>>v^v><v^v<^>v^><>v<<>v>^^v><<<<><^v^v>>^<>^<<>^<v<<>>v<<>><^<<<<^v>^<^v>v>vv<v<v<<>^>v<^<<>v^<vvvv^>v>><<v><v<>v>v>>v^vvv^^>>>v^<^<<^^<<<><v>v^<<v<<<>v<^^<><v<v^^<v>^>v>>v<>^>^^>>^v<<>v^^^>>>^vv<^v<v>^>v>^><>v^^<>^^v^^vv^<^>^<<>><<^>^v>>><<<vvvv><<><v<^v^v<vvv^<><<^<vv><v^v^v^>v>v^<vvv^><^><^<vv><>>v^>^^^<>><v^<^^^<>v<<v<^v>>>^>>v^><<>vvv><^>>v><v><>v>>^>v><<><<>^<>^^^vv><v^>v^^>>^>^<^v<v<^^<^vvvv>v<v>^>v^>^><^<vvvv><^><><<v<>v<v^><^<v^>^v^^<<<<^><^^<^><>>^v<<^<<^vv>v>>v<^<^vv>><v<vv>v<v<v>^v<>^>v<>^v<<<v>>^^v>>><vvv>v^>^v^v>^^^v<vvvv>><^>vvv^<vv^^vv><<<>v<>v>^<vvv^<^<v<v<^vv^^>>vv^<^^v^><^^^^^v<^<v<^>>>vv^v^>^<v>^<><v^<^v>>><^v^<<v<<v<>v>^v<v^v>>^^v<<v<v<<>>>vv>>^v>>^<<<<^><<<><^^>>v<>^vvvv>v^^^>^^^>^<vvvv><^^v<v<>v<^v^v<<v^^^v^<v<^v>v^^<>^>^<^v>vv<v^vv<^<<>v><<^><><^^v<<><^^><>^v>^<><<^<^^<<>vv<>^^<<^>><<<>>vvv>^>v^^v^><<^>v>^>^<^<<>v<^>vv^v^v<>vv<<v>vv<vv><^>v^<>^vv^v^<v<^>>>>v^v><^<><<>vv^<vvv^>>vvv^>v>>><^^vv<vvvv>v<^<^>>^^>^^vv>>><^v<>^v^<<>v^^^<v>^>>^<^<v>>^v<^^^<v>^v>^>>v<vv>>^<v^<<>>^>>><v>v^<<^<v>>^<<^^<>v<^v<^<>v^v>^^v<vvvv>^vv>vvv>v^<^>><v^^vv<<<^>vvvv<>>^^<>v^<><>v<^<>v<>^>v<>vv<v^v>>v<v<^<v^^v^vv^vvv><^^>v>><>>^<^^<>>^>^<v^>>vvv^v><v>>^>^>v><><<><vv^v>v<>^v<^vv^^^<>^^<<^^^v<>><v<^<^<^<^^><v^v<^>v^>vvvv>^^v^>^<v<^^^>>^<<vv^<><><^^^^<<>^<><v>vv^<><^>^^<>v^<>>>v><>vvvvv>v>v^^>^<<vvvv<>vv>>v<<^<>^^^v^<><>>^<<<v<v<>>>><><v>v<v<>>^>^^^^vv^^<<><^^<<vv<^<>v>vv<v<><<<^<<v<<<<>v<>>^<^>^>><v>v>><^^<>><<<><<><v^^v<<><^<^v<v^><^^v<<>><<<<^>v^<v>><v^><v<vvv>v^v^<v><<>>v<><<v>^<>><>>^><>v^v>v<<>v<>v^^><<>>>v<<>>>>^>v>><v<<>>>vv>v>^<^^^<>v<v>^<^^v^vvv^>vv>^<v><vvvv>^<<>vvv<<<vv>^^<^>^>>v>v<<<<<>^^vv^>>v>^<^<v^v^>^v>>v>^v<><>^<^>v>v<<<^^^v>^<<<>vvv^v^^>^>>^>v>v<>^^><>>v>^>v<<<^^^v^<v^vv>><><^<^<><vvv<v^>>^v>vv<^v<<^vv>v^<<v>v>v>^v^>^v<<^v^vv>v<v>^<<><v^>>v<>><v<<<^v<<>vvv^<vv<vvv<<>^vv^^v><^>v^vv<<v^<<^^^<^<>^^<<>v<><<v>^><>^<><<v<v^^>vv<>^<v<^<vvv>vv>v><^^v<>><^v^v><><>><v<v>vv<>>><v^^v<>><<^>>><^^^vvv<<<vv<<^v<<<>><<vv>>>>v<<<<<vv><><v>v^^<<^vv^<vv<>>vv>^<>^v^^<>^^^vv>v^^<v<><v>v<v>>^v<v<>>^<v^^><>v^^^>v^^v<vv><^>v^v^<>v>v<v<^^>>v<^^vv^v<^^^^vv<<><<^>>^^<<v^^<<^>v^>>^^^><^^>^v^v>^<<v<vv<<<v<^^^>^>>^v<>^<^>v>^>^v^<^^^<^vv<v><^^>>v<v>^>^v^>>>>^v>^^<<^<v^v<^<<v<<^><^^<v^<><v>v^<<v^^<><<>>><vv<<><>^<>>>v<<v^^^v^^<<<vv<<^<^<^vv^<><><<^^<^^>v^>^<v<>>v^v<><<v>^^v>^<^<vvv<v>v^v>>>^^<^<v^>^vv<<<v<<>^><><^<>v>>>v<v^<>v>><^^^v^^^v<^^<vv^^^>v>v<>>^^<><>v>^<v<>^>>>><>v>^v>^vv^v<vv<<^^>><v<>^>^^<v<^>^<vvv>><>^<<>>><<<><>^^<<<v<>v^>v>v<v>^^^>^>^v<<>v>vv>><<<v>^^<v><vv<<v^^>^>>^><^>v<^<^v>><^^>v<vv^^><><>^><<><>v^>v<><^^>><>^<^^v<^<<v>><v><<<^^<<v<^vv^v<>><>>>^>v<vvv^>^<><v^><^<<^vv<^v^v^v<>v^^v>v^<^>^vv^>>><<>v^vv^<>^v^><<v^v<v>v^<><>>v^v^><>v^vvv^^^<<^<<v<<v<^vv^>>v^v>^^<v<>><>v>>v^<>^>v>^>><<>v^v><^v>v>>><v<v><^<^^>vv<v><^>^<^>^^v><><v<^^v<<><^<<v^<v<<><^^vvv^v>^>^<>>vv>v^^v^^vv<^^>><v^^vv><^v>v^<<v<^v>vvv<>>^v><<>^v<<<>^><^vv><<^^<v^>v<<v>^vv<>^v>>>><<<<^^<^v>^<^^<^<^^>>^^v>^^^^v^^^<<>^^vv<<v^^><v>><^<<><>^>v<>>v^^^>^v^^v^<v^v>v>>>>>^v>^>^^<vvv^^<v^<<<v<<>v>><^^^v<<^^<v>>^<^<^><^<<v^v><<vv<^<>>v>v>^v<><<v>^>vv^v<v>v><^<v>><>^<vv<v^^^^v<^^>><<^^>v>v>^^^<>v>^v^^>vv^vv<^^>><>^>^<>v>><>^v<<v>v>^><^^^v^<vv><<^v^>v^>vv>v^<>v><vv><^v>v<><v^v^v<^v<>^v<v^<<><<v>>^v><v>^^<>vvv^>^<<v^>><^>><^<>^v<v<v<^vvv<><<^v^<v>><<<v>^<^<v>v>^vv^v>v<^^vv<<vvv^<v>><>vv^>v<<>v<vvvv>>v>^^>>><<<^>^vv>><v>^^^>v<^vv<>v<<<v<<<<v>>>>^<^^^^>v<^^<><v>v>v<v^>vv^>v>v<^>^v^<>v>>vvv>^^><^vvv>><>>>^<<^<v<>>>v^^><v<v>>^><>v<^^v^<<v><>^<>>><^v^v>>>^vvvv^<><<<v<^>>v>^v^<v<v<<^<<v^vv^v>v<v<>>v<v^<<<><v^>><^<<^>^^><v>v<^v^<^>v>^<<v>v^<>v^<>vv^<>^>^>v^>^vv<>^^<<>>v<>^v<><v^><><<<vv>v>v^>vv^><<<<v>^v<><>^^<vv>v^^v^^^<v<^^><v^v<>><v<vv>^<>>><vv<^v<<>>^><>>v<v^v^>>>v<<>v<<<<<<<^v<<^^^v<^v<>v^^<<<^<>>v^vv<v>^<^^<^^<<^>vv><^<^^v<<<^><^v<^><>v<vv^>^v^^>>><<vv^^v><^<<^<>>^>>^<<<<v^vv<>>>v>^v>><>v>>v>><>v>><^^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x, y = compute_position_from(move)

def compute_position_from(move)
x, y = 0, 0

do the case thing here

return x, y
end