Created
December 25, 2017 05:01
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use std::cmp::max; | |
use std::collections::{HashMap, HashSet}; | |
use std::iter; | |
const _SAMPLE_INPUT: &str = "\ | |
0/2 | |
2/2 | |
2/3 | |
3/4 | |
3/5 | |
0/1 | |
10/1 | |
9/10\ | |
"; | |
const _REAL_INPUT: &str = "\ | |
31/13 | |
34/4 | |
49/49 | |
23/37 | |
47/45 | |
32/4 | |
12/35 | |
37/30 | |
41/48 | |
0/47 | |
32/30 | |
12/5 | |
37/31 | |
7/41 | |
10/28 | |
35/4 | |
28/35 | |
20/29 | |
32/20 | |
31/43 | |
48/14 | |
10/11 | |
27/6 | |
9/24 | |
8/28 | |
45/48 | |
8/1 | |
16/19 | |
45/45 | |
0/4 | |
29/33 | |
2/5 | |
33/9 | |
11/7 | |
32/10 | |
44/1 | |
40/32 | |
2/45 | |
16/16 | |
1/18 | |
38/36 | |
34/24 | |
39/44 | |
32/37 | |
26/46 | |
25/33 | |
9/10 | |
0/29 | |
38/8 | |
33/33 | |
49/19 | |
18/20 | |
49/39 | |
18/39 | |
26/13 | |
19/32\ | |
"; | |
const INPUT: &str = _REAL_INPUT; | |
type ComponentId = usize; | |
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)] | |
struct Half { | |
component_id: ComponentId, | |
half_id: usize, // 0 or 1 | |
} | |
impl Half { | |
fn opposite(self) -> Self { | |
Half { | |
component_id: self.component_id, | |
half_id: 1 - self.half_id, | |
} | |
} | |
} | |
fn strongest_from_half( | |
half: Half, | |
seen: &mut HashSet<ComponentId>, | |
edges: &HashMap<Half, Vec<Half>>, | |
components: &Vec<[u64; 2]>, | |
) -> u64 { | |
assert!(seen.insert(half.component_id)); | |
let mut best = 0; | |
for &other_half in &edges[&half.opposite()] { | |
if seen.contains(&other_half.component_id) { continue; } | |
best = max( | |
best, | |
strongest_from_half(other_half, seen, edges, components), | |
); | |
seen.remove(&other_half.component_id); | |
} | |
/* | |
let strongest_edge = edges | |
.get(&half) | |
.unwrap() | |
.iter() | |
.filter(|other_half| !seen.contains(&other_half.component_id)) | |
.map(|&other_half| { | |
strongest_from_half(other_half, seen, edges, components) | |
}) | |
.max() | |
.unwrap_or(0); | |
*/ | |
best + components[half.component_id].iter().cloned().sum::<u64>() | |
} | |
fn main() { | |
let components: Vec<[u64; 2]> = INPUT | |
.split('\n') | |
.map(|line| { | |
let mut parts = line.split('/').map(|n| n.parse::<u64>().unwrap()); | |
[parts.next().unwrap(), parts.next().unwrap()] | |
}) | |
.collect(); | |
let halves: Vec<(Half, u64)> = components | |
.iter() | |
.enumerate() | |
.flat_map(|(i, neighbor)| { | |
iter::once(i) | |
.cycle() | |
.zip(neighbor.iter().cloned().enumerate()) | |
.map(|(component_id, (half_id, val))| { | |
(Half { component_id, half_id }, val) | |
}) | |
}) | |
.collect(); | |
let mut edges: HashMap<Half, Vec<Half>> = HashMap::new(); | |
for &(half, val) in &halves { | |
let neighbors = edges.entry(half).or_insert(Vec::new()); | |
for &(other_half, other_val) in &halves { | |
if other_half.component_id == half.component_id { continue; } | |
if val == other_val { | |
neighbors.push(other_half); | |
} | |
} | |
} | |
// println!("{:#?}", edges); | |
let starts = halves | |
.iter() | |
.filter(|&&(_, val)| val == 0) | |
.map(|&(half, _)| half); | |
let strongest = starts.map(|starting_half| { | |
let mut seen = HashSet::new(); | |
strongest_from_half(starting_half, &mut seen, &edges, &components) | |
}).max().unwrap(); | |
println!("{}", strongest); | |
} |
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