I’m still one day behind but here goes my day 8. I struggled at puzzle 2 getting my ranges right. Yup, and I had the same issue with counting the taller tree.
defmodule ExAOC2022.Day8 do
@input "./lib/day8_input.txt"
def puzzle1() do
lines = file_by_line(@input)
grid = Enum.map(lines, &(String.split(&1, "", trim: true)))
rows_num = length(lines)
cols_num = hd(grid) |> length
for i <- 0..rows_num-1, j <- 0..cols_num-1, reduce: 0 do
acc ->
if visible?(grid, i, j, rows_num, cols_num), do: acc + 1, else: acc
end
end
def puzzle2() do
lines = file_by_line(@input)
grid = Enum.map(lines, &(String.split(&1, "", trim: true)))
rows_num = length(lines)
cols_num = hd(grid) |> length
for i <- 1..rows_num-2, j <- 1..cols_num-2, reduce: 0 do
acc ->
score = scenic_score(grid, i, j, rows_num-1, cols_num-1)
if score > acc, do: score, else: acc
end
end
defp visible?(grid, x, y, max_x, max_y) do
v = val(grid, x, y)
cond do
# edge
x == 0 or y == 0 or x == (max_x - 1) or y == (max_y - 1) ->
true
# up
max_num_y(grid, x, 0, y-1) < v ->
true
# down
max_num_y(grid, x, y+1, max_y-1) < v ->
true
# left
max_num_x(grid, y, 0, x-1) < v ->
true
# right
max_num_x(grid, y, x+1, max_x-1) < v ->
true
true ->
false
end
end
defp scenic_score(grid, x, y, max_x, max_y) do
v = val(grid, x, y)
up_trees = Enum.map(y-1..0//-1, &val(grid, x, &1)) |> dist(v)
left_trees = Enum.map(x-1..0//-1, &val(grid, &1, y)) |> dist(v)
down_trees = Enum.map(y+1..max_y, &val(grid, x, &1)) |> dist(v)
right_trees = Enum.map(x+1..max_x, &val(grid, &1, y)) |> dist(v)
up_trees * down_trees * left_trees * right_trees
end
defp dist(trees, our_tree) do
Enum.reduce_while(trees, 0, fn tree, score ->
if tree >= our_tree, do: {:halt, score + 1}, else: {:cont, score + 1}
end)
end
defp max_num_y(grid, x, from, to), do:
Enum.map(from..to, &val(grid, x, &1)) |> Enum.max()
defp max_num_x(grid, y, from, to), do:
Enum.map(from..to, &val(grid, &1, y)) |> Enum.max()
defp int(s), do: String.to_integer(s)
defp val(grid, x, y) do
get_in(grid, [Access.at(y), Access.at(x)]) |> int
end
defp file_by_line(file) do
file
|> File.read!()
|> String.split(~r/\R/, trim: true)
end
end
