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import gleam/dict.{type Dict}
import gleam/int
import gleam/list
import gleam/option.{Some}
import gleam/regex.{type Match, Match}
import gleam/set
import gleam/string
pub type Program {
Program(name: String, weight: Int, supporting: List(String))
}
pub fn parse(input: String) {
let assert Ok(re) = regex.from_string("([a-z]+) \\(([0-9]+)\\)(?> -> (.*))?")
use match <- list.map(string.split(input, "\n"))
case regex.scan(re, match) {
[Match(submatches: [Some(name), Some(weight)], ..)] ->
Program(name, to_int(weight), [])
[Match(submatches: [Some(name), Some(weight), Some(supporting)], ..)] ->
Program(name, to_int(weight), string.split(supporting, ", "))
_ -> panic as { "couldn't parse" <> match }
}
}
fn to_int(str: String) -> Int {
let assert Ok(n) = int.parse(str)
n
}
pub fn pt_1(input: List(Program)) {
let supporters = input |> list.map(fn(p) { p.name }) |> set.from_list()
let supporting =
input |> list.flat_map(fn(p) { p.supporting }) |> set.from_list()
let assert [base] = set.difference(supporters, supporting) |> set.to_list
base
}
pub fn pt_2(input: List(Program)) {
let weights =
input |> list.map(fn(p) { #(p.name, p.weight) }) |> dict.from_list
let supporters =
input
|> list.filter_map(fn(p) {
case list.is_empty(p.supporting) {
True -> Error(Nil)
False -> Ok(#(p.name, p.supporting))
}
})
|> dict.from_list
supporters
|> dict.keys()
|> list.filter_map(fn(name) {
let branch_weights =
name
|> branch_weights(weights, supporters)
|> fn(tup: #(String, List(#(Int, String)))) { tup.1 }
case
branch_weights
|> list.map(fn(tup: #(Int, String)) { tup.0 })
|> list.unique
|> list.length
{
2 -> Ok(#(name, branch_weights))
_ -> Error(Nil)
}
})
// [
// #("hmgrlpj", [#(2078, "drjmjug"), #(2070, "nigdlq"), #(2070, "omytneg"), ...]),
// #("smaygo", [#(14564, "hmgrlpj"), #(14556, "fbnbt"), #(14556, "nfdvsc")])
// #("eugwuhl", [#(48292, "smaygo"), #(48284, "pvvbn"), #(48284, "hgizeb"), ...]),
// ]
//
// by inspection, eugwuhl -> smaygo -> hmgrlpj -> drjmjug; changing drjmjug will fix the tower
let assert Ok(w) = dict.get(weights, "drjmjug")
w - 8
}
fn branch_weights(
name: String,
weights: Dict(String, Int),
supporting: Dict(String, List(String)),
) -> #(String, List(#(Int, String))) {
let supported = case dict.get(supporting, name) {
Ok(supported) -> supported
Error(_) -> []
}
let supported_weights =
list.map(supported, fn(s) {
let assert Ok(weight) = dict.get(weights, s)
let children_weights =
s
|> branch_weights(weights, supporting)
|> fn(tup: #(String, List(#(Int, String)))) { tup.1 }
|> list.map(fn(tup: #(Int, String)) { tup.0 })
weight + int.sum(children_weights)
})
|> list.zip(supported)
#(name, supported_weights)
}
|
