1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
|
import adglent.{First, Second}
import gleam/int
import gleam/io
import gleam/dict.{type Dict}
import gleam/list
import gleam/option.{type Option, None, Some}
import gleam/string
import gleam/set.{type Set}
import gleam/bool
import utilities/array2d.{type Array2D, type Posn, Posn}
type Path {
Unknown
Straight
Junction
}
type Route {
Route(to: Posn, distance: Int)
}
fn append_to_key(v: Option(List(a)), new: a) -> List(a) {
case v {
None -> [new]
Some(xs) -> [new, ..xs]
}
}
fn first_parse_path(c: String) -> Result(Path, Nil) {
case c {
"#" -> Error(Nil)
_ -> Ok(Unknown)
}
}
fn junction_neighbors(p: Posn) -> List(Posn) {
[Posn(..p, r: p.r + 1), Posn(..p, c: p.c + 1)]
}
fn mark_junctions(trails: Array2D(Path)) -> Array2D(Path) {
use trail, _ <- dict.map_values(trails)
let valid_neighbors =
trail
|> array2d.ortho_neighbors
|> list.filter(dict.has_key(trails, _))
case list.length(valid_neighbors) {
2 -> Straight
_ -> Junction
}
}
fn start_walking_to_next_junction(
start: Posn,
next: Posn,
trails: Array2D(Path),
) {
let seen =
set.new()
|> set.insert(start)
|> set.insert(next)
walk_to_next_junction(start, next, 1, seen, trails)
}
fn walk_to_next_junction(
start: Posn,
current: Posn,
length: Int,
seen: Set(Posn),
trails: Array2D(Path),
) -> #(Posn, Route) {
let assert [next] =
current
|> array2d.ortho_neighbors
|> list.filter(fn(n) { dict.has_key(trails, n) && !set.contains(seen, n) })
case dict.get(trails, next) {
Ok(Junction) -> #(start, Route(to: next, distance: length + 1))
_ -> {
let seen = set.insert(seen, current)
walk_to_next_junction(start, next, { length + 1 }, seen, trails)
}
}
}
fn find_routes(junctions, trails) {
use junction <- list.flat_map(junctions)
use neighbor <- list.filter_map(junction_neighbors(junction))
case dict.has_key(trails, neighbor) {
True -> Ok(start_walking_to_next_junction(junction, neighbor, trails))
False -> Error(Nil)
}
}
fn generate_routes(
junctions: List(Posn),
trails: Array2D(Path),
) -> Dict(Posn, List(Route)) {
use acc, #(from, route) <- list.fold(
find_routes(junctions, trails),
dict.new(),
)
dict.update(acc, from, append_to_key(_, route))
}
fn generate_2way_routes(
junctions: List(Posn),
trails: Array2D(Path),
) -> Dict(Posn, List(Route)) {
use acc, #(from, route) <- list.fold(
find_routes(junctions, trails),
dict.new(),
)
acc
|> dict.update(from, append_to_key(_, route))
|> dict.update(route.to, append_to_key(_, Route(from, route.distance)))
}
fn dfs(routes, from, to) {
let seen = set.insert(set.new(), from)
do_dfs(routes, from, to, 0, seen)
}
fn do_dfs(
routes: Dict(Posn, List(Route)),
from: Posn,
to: Posn,
acc: Int,
seen: Set(Posn),
) -> Int {
use <- bool.guard(to == from, acc)
let assert Ok(all_routes) = dict.get(routes, from)
let neighbors = list.filter(all_routes, fn(r) { !set.contains(seen, r.to) })
case neighbors {
[] -> 0
neighbors ->
list.fold(neighbors, acc, fn(inner_acc, n) {
let score =
do_dfs(routes, n.to, to, acc + n.distance, set.insert(seen, n.to))
int.max(score, inner_acc)
})
}
}
fn solve_using(
input: String,
using: fn(List(Posn), Dict(Posn, Path)) -> Dict(Posn, List(Route)),
) -> Int {
let min_row = 0
let max_row = list.length(string.split(input, "\n")) - 1
let trails =
input
|> array2d.parse_grid_using(first_parse_path)
|> mark_junctions
let junctions =
trails
|> dict.filter(fn(_, v) { v == Junction })
|> dict.keys
let assert Ok(start) = list.find(junctions, fn(j) { j.r == min_row })
let assert Ok(end) = list.find(junctions, fn(j) { j.r == max_row })
let routes = using(junctions, trails)
dfs(routes, start, end)
}
pub fn part1(input: String) {
solve_using(input, generate_routes)
}
pub fn part2(input: String) {
solve_using(input, generate_2way_routes)
}
pub fn main() {
let assert Ok(part) = adglent.get_part()
let assert Ok(input) = adglent.get_input("23")
case part {
First ->
part1(input)
|> adglent.inspect
|> io.println
Second ->
part2(input)
|> adglent.inspect
|> io.println
}
}
|
