Codility Task LOGO turtle - SegmentCrossing

logo_codility.rb

def intersects?(p0, p1, p2, p3)
  s1_x = p1[0] - p0[0]
  s1_y = p1[1] - p0[1]
  s2_x = p3[0] - p2[0]
  s2_y = p3[1] - p2[1]

  denom = s1_x * s2_y - s2_x * s1_y
  # if denom == 0 lines are parallel
  # TODO: aditional check if they overlap
  return false if (denom == 0)

  denom_positive = denom > 0

  s3_x = p0[0] - p2[0]
  s3_y = p0[1] - p2[1]

  s_numer = s1_x * s3_y - s1_y * s3_x
  # s must be positive for posible colition
  # s = s_numer / demom
  return false if (s_numer < 0) == denom_positive

  t_numer = s2_x * s3_y - s2_y * s3_x
  # t must be positive for posible colition
  # t = t_numer / demom
  return false if (t_numer < 0) == denom_positive

  # both t and s must be <= 1 so |s_numer| <= |denom| AND |t_numer| <= |denom|
  (s_numer <= denom) == denom_positive && (t_numer <= denom) == denom_positive
end

def solution(a)
  path = [[0, 0]]
  directions = [[0, 1], [1, 0], [0, -1], [-1, 0]]

  a.each.with_index do |steps, solution_index|
    position = path.last
    direction = directions[solution_index % 4]

    path << [position[0] + steps * direction[0], position[1] + steps * direction[1]]

    next if path.size <= 4

    end_segment_1   = path[path.size - 1]
    # Border case when the path ends at the beginning
    return solution_index + 1 if end_segment_1 == [0, 0]
    start_segment_1 = path[path.size - 2]

    # First check is 4 moves ago
    start_segment_0 = path[path.size - 5]
    end_segment_0   = path[path.size - 4]

    if intersects?(start_segment_0, end_segment_0, start_segment_1, end_segment_1)
      return solution_index + 1
    end
    
    next if path.size <= 6
    # Second check is 6 moves ago
    start_segment_0 = path[path.size - 7]
    end_segment_0   = path[path.size - 6]
    
    if intersects?(start_segment_0, end_segment_0, start_segment_1, end_segment_1)
      return solution_index + 1
    end
  end
  0
end

solution [1, 3, 2, 5, 4, 4, 6, 3, 2] #=> 7
solution [1, 1, 1, 2] #=> 4
solution [1, 1, 2, 1, 1]  #=> 5
solution [4, 4, 5, 7, 8, 6, 5] #=> 7
solution [1, 1, 2, 2, 4, 2, 1, 1, 2, 5, 10] #=> 9
solution [1, 1, 5, 3, 3, 2, 2, 1, 1, 3] #=> 10