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
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
|
use std::collections::{HashMap, HashSet};
static DAY: u8 = 12;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", fencing_price(&input, false));
println!("{DAY}b: {}", fencing_price(&input, true));
}
#[derive(Eq, PartialEq, Copy, Clone, Hash)]
struct Position {
x: isize,
y: isize,
}
fn count_fences(region: &HashSet<Position>) -> usize {
let mut total_fences = 0;
for pos in region {
/* every plot has 4 fences, except it has neighbors of the same type */
let mut fences = 4;
for diff in [(-1, 0), (1, 0), (0, -1), (0, 1)] {
let neighbor = Position { x: pos.x + diff.0, y: pos.y + diff.1 };
if region.contains(&neighbor) {
fences -= 1;
}
}
total_fences += fences;
}
total_fences
}
fn count_sides(region: &HashSet<Position>) -> usize {
let mut horizontal = HashSet::new();
let mut vertical = HashSet::new();
let mut min_pos = Position { x: isize::MAX, y: isize::MAX };
let mut max_pos = Position { x: isize::MIN, y: isize::MIN };
for pos in region {
min_pos.x = min_pos.x.min(pos.x);
min_pos.y = min_pos.y.min(pos.y);
max_pos.x = max_pos.x.max(pos.x);
max_pos.y = max_pos.y.max(pos.y);
let neighbor = Position { x: pos.x, y: pos.y + 1 };
if !region.contains(&neighbor) {
horizontal.insert((neighbor, 1));
max_pos.y = max_pos.y.max(neighbor.y);
}
let neighbor = Position { x: pos.x, y: pos.y - 1 };
if !region.contains(&neighbor) {
horizontal.insert((neighbor, 0));
min_pos.y = min_pos.y.min(neighbor.y);
}
let neighbor = Position { x: pos.x + 1, y: pos.y };
if !region.contains(&neighbor) {
vertical.insert((neighbor, 1));
max_pos.x = max_pos.x.max(neighbor.x);
}
let neighbor = Position { x: pos.x - 1, y: pos.y };
if !region.contains(&neighbor) {
vertical.insert((neighbor, 0));
min_pos.x = min_pos.x.min(neighbor.x);
}
}
let mut sides = 0;
for separator in [0, 1] {
for x in min_pos.x ..= max_pos.x {
let mut is_side = false;
for y in min_pos.y ..= max_pos.y {
let check = Position { x, y };
if is_side && !vertical.contains(&(check, separator)) {
is_side = false;
sides += 1;
}
if !is_side && vertical.contains(&(check, separator)) {
is_side = true;
}
}
}
}
for separator in [0, 1] {
for y in min_pos.y ..= max_pos.y {
let mut is_side = false;
for x in min_pos.x ..= max_pos.x {
let check = Position { x, y };
if is_side && !horizontal.contains(&(check, separator)) {
is_side = false;
sides += 1;
}
if !is_side && horizontal.contains(&(check, separator)) {
is_side = true;
}
}
}
}
sides
}
fn find_region(plots: &HashMap<Position, char>, pos: Position, visited: &mut HashSet<Position>) -> HashSet<Position> {
let mut region = HashSet::new();
if visited.contains(&pos) {
return region;
}
let plot_type = plots.get(&pos).unwrap();
region.insert(pos);
visited.insert(pos);
for diff in [(-1, 0), (1, 0), (0, -1), (0, 1)] {
let neighbor = Position { x: pos.x + diff.0, y: pos.y + diff.1 };
if let Some(t) = plots.get(&neighbor) {
if t == plot_type {
for r in find_region(plots, neighbor, visited) {
region.insert(r);
}
}
}
}
region
}
fn find_regions(plots: &HashMap<Position, char>) -> HashMap<char, Vec<HashSet<Position>>> {
let mut regions = HashMap::new();
let mut visited = HashSet::new();
for (pos, c) in plots {
if visited.contains(pos) {
continue;
}
let region = find_region(plots, *pos, &mut HashSet::new());
for plot in ®ion {
visited.insert(*plot);
}
regions.entry(*c).or_insert(Vec::new()).push(region);
}
regions
}
fn fencing_price(input: &[String], with_discount: bool) -> usize {
let mut plots = HashMap::new();
for (y, line) in input.iter().enumerate() {
for (x, c) in line.chars().enumerate() {
let pos = Position { x: x as isize, y: y as isize };
plots.insert(pos, c);
}
}
let all_regions = find_regions(&plots);
let mut total_price = 0;
for regions in all_regions.values() {
for region in regions {
let area = region.len();
let fences = if !with_discount {
count_fences(region)
} else {
count_sides(region)
};
total_price += area * fences;
}
}
total_price
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"AAAA",
"BBCD",
"BBCC",
"EEEC",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input, false), 140);
assert_eq!(fencing_price(&input, true), 80);
let input = [
"OOOOO",
"OXOXO",
"OOOOO",
"OXOXO",
"OOOOO",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input, false), 772);
assert_eq!(fencing_price(&input, true), 436);
let input = [
"RRRRIICCFF",
"RRRRIICCCF",
"VVRRRCCFFF",
"VVRCCCJFFF",
"VVVVCJJCFE",
"VVIVCCJJEE",
"VVIIICJJEE",
"MIIIIIJJEE",
"MIIISIJEEE",
"MMMISSJEEE",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input, false), 1930);
let input = [
"EEEEE",
"EXXXX",
"EEEEE",
"EXXXX",
"EEEEE",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input, true), 236);
let input = [
"AAAAAA",
"AAABBA",
"AAABBA",
"ABBAAA",
"ABBAAA",
"AAAAAA",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(fencing_price(&input, true), 368);
}
}
|
