Advent of Code (AOC) 2017 Day 3

day3.ex

  defmodule Day3 do
    # This does more work than required but is still O(1)
    # diagonal low right is even square root                                                           
    def start1( val ) do
      col_height = :math.sqrt( val ) |> Float.ceil |> trunc
      col_height = if Integer.mod( col_height, 2 ) == 0, do: col_height+1, else: col_height
      low_right_corner = :math.pow( col_height, 2 ) |> trunc
      distance = low_right_corner - val
      ring_length = col_height * 4 - 4

      side = distance / ring_length
      side_length = Integer.floor_div(ring_length, 4 )
      side_pos = Integer.mod( distance, side_length)

      quarter = Integer.floor_div( ring_length, 8 )
      #steps_to_middle = Integer.mod( distance , quarter )                                             
      hside = Integer.floor_div( side_length, 2 )
      steps_to_middle = hside - side_pos

      before = steps_to_middle > 0
      side_name = cond do
        side == 0.0 -> { :corner_se, quarter, :up, :left }
        side == 0.25 -> { :corner_sw, quarter, :up, :right }
        side == 0.50 -> { :corner_nw, quarter, :down, :right }
        side == 0.75 -> { :corner_ne, quarter, :down, :left }
        side < 0.25 -> { :bottom, steps_to_middle, before && :left || :right, :up }
        side < 0.50 -> { :left, steps_to_middle, before && :up || :down, :right }
        side < 0.75 -> { :top, steps_to_middle, before && :right || :left, :down }
        true -> { :right, steps_to_middle, before && :down || :up, :left }
      end
      steps_to_center = Integer.floor_div( col_height - 1, 2 )
      [ col_hight: col_height,
        low_right_corner: low_right_corner,
        distance: distance,
        side: side,
        side_pos: side_pos,
        side_name: side_name,
        ring_length: ring_length,
        steps_to_center: steps_to_center,
        steps_to_middle: steps_to_middle,
        quarter: quarter,
        side_length: side_length,
        steps_required: abs( steps_to_middle ) + steps_to_center,
      ]
    end
  end