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import gleam/list
import gleam/io
import gleam/int
import gleam/result as res
import gleam/string as str
import gleam/function as fun
import gleam/iterator as iter
import gleam/set.{Set}
import ext/intx
import ext/iteratorx as iterx
import util/input_util
import util/pos.{Pos}
const starting_pos = #(0, 0)
const base_slope = #(3, 1)
const all_slopes = [#(1, 1), base_slope, #(5, 1), #(7, 1), #(1, 2)]
type Area {
Area(trees: Set(Pos), cycle: Int, height: Int)
}
fn parse_area(from text: String) -> Area {
let lines = str.split(text, on: "\n")
let trees =
list.index_fold(
over: lines,
from: set.new(),
with: fn(prev, line, y) {
line
|> str.to_graphemes
|> list.index_map(with: fn(x, grapheme) {
case grapheme {
"#" -> Ok(#(x, y))
_ -> Error(Nil)
}
})
|> list.filter_map(with: fun.identity)
|> set.from_list
|> set.union(prev)
},
)
let assert Ok(cycle) =
lines
|> list.first
|> res.map(with: str.length)
let height = list.length(lines)
Area(trees, cycle, height)
}
fn has_tree(in area: Area, at pos: Pos) -> Bool {
set.contains(area.trees, #(pos.0 % area.cycle, pos.1))
}
fn is_valid(pos: Pos, in area: Area) -> Bool {
intx.is_between(pos.1, 0, and: area.height - 1)
}
fn tree_count(in area: Area, with slope: Pos) -> Int {
starting_pos
|> iter.iterate(with: pos.add(_, slope))
|> iter.take_while(satisfying: is_valid(_, in: area))
|> iterx.count(satisfying: has_tree(in: area, at: _))
}
fn part1(text: String) -> Int {
text
|> parse_area
|> tree_count(with: base_slope)
}
fn part2(text: String) -> Int {
let area = parse_area(from: text)
all_slopes
|> list.map(with: tree_count(in: area, with: _))
|> int.product
}
pub fn main() -> Nil {
let test = input_util.read_text("test03")
let assert 7 = part1(test)
let assert 336 = part2(test)
let input = input_util.read_text("day03")
io.debug(part1(input))
io.debug(part2(input))
Nil
}
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