69 lines
1.6 KiB
Gleam
69 lines
1.6 KiB
Gleam
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import gleam/bool
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import gleam/dict.{type Dict}
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import gleam/int
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import gleam/io
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import gleam/iterator
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import gleam/list.{filter, filter_map, fold, map, reverse}
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import gleam/string
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import stdin.{stdin}
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pub fn main() {
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stdin()
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|> read_input
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|> calculate_trails
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|> io.debug
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}
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fn calculate_trails(topomap: Dict(#(Int, Int), Int)) -> Int {
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topomap
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|> find_trailheads
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|> map(fn(x) { count_trails_loop(topomap, x, 0) })
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|> map(list.length)
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|> fold(0, int.add)
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}
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fn count_trails_loop(
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topomap: Dict(#(Int, Int), Int),
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pos: #(Int, Int),
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offset: Int,
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) -> List(#(Int, Int)) {
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let #(x, y) = pos
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case dict.get(topomap, pos) {
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Ok(9) if offset == 9 -> {
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[pos]
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}
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Ok(n) if n == offset ->
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[
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count_trails_loop(topomap, #(x, y - 1), offset + 1),
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count_trails_loop(topomap, #(x, y + 1), offset + 1),
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count_trails_loop(topomap, #(x - 1, y), offset + 1),
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count_trails_loop(topomap, #(x + 1, y), offset + 1),
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]
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|> filter(fn(x) { x |> list.is_empty |> bool.negate })
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|> list.flatten
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|> list.unique
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_ -> []
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}
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}
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fn find_trailheads(topomap: Dict(#(Int, Int), Int)) -> List(#(Int, Int)) {
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topomap |> dict.filter(fn(_, v) { v == 0 }) |> dict.keys
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}
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fn read_input(it: iterator.Iterator(String)) -> Dict(#(Int, Int), Int) {
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it
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|> iterator.fold([], fn(acc, line) {
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case string.trim(line) {
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"" -> acc
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str -> {
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[str |> string.to_graphemes |> filter_map(int.parse), ..acc]
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}
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}
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})
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|> reverse
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|> list.index_fold(dict.new(), fn(acc, line, y) {
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line
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|> list.index_fold(acc, fn(dic, num, x) { dict.insert(dic, #(x, y), num) })
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})
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}
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