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import adglent.{First, Second}
import gleam/bool
import gleam/dict.{type Dict}
import gleam/list
import gleam/int
import gleam/io
import gleam/set.{type Set}
import gleam/string
type Posn {
Posn(row: Int, col: Int)
}
fn add_posns(p1: Posn, p2: Posn) -> Posn {
Posn(p1.row + p2.row, p1.col + p2.col)
}
type PipeGrid =
Dict(Posn, String)
const north = Posn(-1, 0)
const south = Posn(1, 0)
const east = Posn(0, 1)
const west = Posn(0, -1)
const initial_directions = [
#(north, ["|", "7", "F"]),
#(south, ["|", "J", "L"]),
#(east, ["-", "J", "7"]),
#(west, ["-", "F", "L"]),
]
fn pipe_neighbors(pipe: String) -> List(Posn) {
case pipe {
"|" -> [north, south]
"-" -> [east, west]
"L" -> [north, east]
"F" -> [south, east]
"7" -> [south, west]
"J" -> [north, west]
_ -> panic as "bad pipe"
}
}
fn make_grid(input: String) -> PipeGrid {
{
use r, row <- list.index_map(string.split(input, "\n"))
use c, col <- list.index_map(string.to_graphemes(row))
#(Posn(r, c), col)
}
|> list.flatten
|> dict.from_list
}
fn valid_start_direction(grid: PipeGrid, s: Posn) {
let assert [dir, ..] = {
use d <- list.filter_map(initial_directions)
let #(delta, valids) = d
let neighbor = add_posns(s, delta)
case dict.get(grid, neighbor) {
Ok(pipe) ->
case list.contains(valids, pipe) {
True -> Ok(neighbor)
False -> Error(Nil)
}
Error(_) -> Error(Nil)
}
}
dir
}
fn to_next_pipe(current: Posn, grid: PipeGrid, acc: List(Posn)) {
let assert [prev, ..] = acc
let assert Ok(pipe) = dict.get(grid, current)
use <- bool.guard(pipe == "S", [current, ..acc])
let assert [next] = {
pipe
|> pipe_neighbors
|> list.filter_map(fn(p) {
case add_posns(p, current) {
neighbor if neighbor == prev -> Error(Nil)
neighbor -> Ok(neighbor)
}
})
}
to_next_pipe(next, grid, [current, ..acc])
}
pub fn part1(input: String) {
let grid =
input
|> make_grid
let assert Ok(s) =
grid
|> dict.filter(fn(_, v) { v == "S" })
|> dict.keys
|> list.first
grid
|> valid_start_direction(s)
|> to_next_pipe(grid, [s])
|> list.length
|> fn(i) { { { i - 1 } / 2 } }
|> string.inspect
}
fn trace_ray(p: Posn, loop: Set(Posn), grid: PipeGrid) -> Bool {
use <- bool.guard(set.contains(loop, p), False)
int.is_odd(count_crossings(p, loop, grid, 0, ""))
}
fn count_crossings(
p: Posn,
loop: Set(Posn),
grid: PipeGrid,
acc: Int,
corner: String,
) {
let maybe_cell = dict.get(grid, p)
use <- bool.guard(maybe_cell == Error(Nil), acc)
let assert Ok(cell) = maybe_cell
let next = add_posns(p, east)
case set.contains(loop, p) {
False -> count_crossings(next, loop, grid, acc, corner)
True ->
case corner, cell {
_, "|" -> count_crossings(next, loop, grid, acc + 1, corner)
_, "F" | _, "L" -> count_crossings(next, loop, grid, acc, cell)
"F", "J" | "L", "7" -> count_crossings(next, loop, grid, acc + 1, "")
"F", "7" | "L", "J" -> count_crossings(next, loop, grid, acc, "")
_, _ -> count_crossings(next, loop, grid, acc, corner)
}
}
}
pub fn part2(input: String) {
let grid =
input
|> make_grid
let assert Ok(s) =
grid
|> dict.filter(fn(_, v) { v == "S" })
|> dict.keys
|> list.first
let loop_pipes =
grid
|> valid_start_direction(s)
|> to_next_pipe(grid, [s])
|> set.from_list
grid
|> dict.keys
|> list.filter(trace_ray(_, loop_pipes, grid))
|> list.length()
|> string.inspect
}
pub fn main() {
let assert Ok(part) = adglent.get_part()
let assert Ok(input) = adglent.get_input("10")
case part {
First ->
part1(input)
|> adglent.inspect
|> io.println
Second ->
part2(input)
|> adglent.inspect
|> io.println
}
}
|
