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|
use std::io;
use std::io::BufRead;
use std::collections::BinaryHeap;
use std::collections::HashSet;
const MOD: usize = 20183;
pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
let mut lines = reader.lines();
let depth: usize = lines.next().unwrap().unwrap().split(' ').skip(1).next().unwrap().parse().unwrap();
let target: (usize, usize) = {
let line = lines.next().unwrap().unwrap();
let mut iter = line.split(' ').skip(1).next().unwrap().split(',');
let x = iter.next().unwrap().parse().unwrap();
let y = iter.next().unwrap().parse().unwrap();
(x, y)
};
// I believe the route can never go beyond target / 2 * 7 from the entrance, but
// I don't trust the factor 2 and I don't want to deal with rounding issues.
let w = 8 * target.0;
let h = 8 * target.1;
let terrain = {
let mut erosion = vec![0; w * h];
for x in 0..w {
erosion[x] = (16807 * x + depth) % MOD;
}
for y in 1..h {
erosion[w*y] = (48271 * y + depth) % MOD;
}
for y in 1..h {
for x in 1..w {
if x == target.0 && y == target.1 {
erosion[w*y+x] = depth % MOD;
} else {
erosion[w*y+x] = (erosion[w*y+x-1] * erosion[w*(y-1)+x] + depth) % MOD;
}
}
}
erosion.iter().map(|val| val % 3).collect::<Vec<_>>()
};
let part1 = {
let mut total_risk = 0;
for y in 0..target.1+1 {
for x in 0..target.0+1 {
total_risk += terrain[w*y+x];
}
}
total_risk
};
let w = w as isize;
let h = h as isize;
// terrain = {0 = rocky, 1 = wet, 2 = narrow}
// tool = {0 = neither, 1 = torch, 2 = climbing gear}
let can_traverse = |tool, (x, y)| x >= 0 && y >= 0 && match terrain[(w*y+x) as usize] {
0 => tool >= 1,
1 => tool != 1,
2 => tool != 2,
_ => unreachable!(),
};
let neighbours = |(x, y)| [(x-1, y), (x, y-1), (x+1, y), (x, y+1)];
// for &pt in neighbours((0, 0)).iter().filter(|&&pt| can_traverse(0, pt)) {
// println!("{:?}", pt);
// }
let mut pqu = BinaryHeap::new();
pqu.push((-0, 1, 0, 0));
let mut distmap = vec![isize::max_value(); (3 * w * h) as usize]; // w*h*tool + w*y + x
distmap[(w*h*1 + w*0 + 0) as usize] = 0;
// let mut parent = vec![(-1, -1, -1); (3 * w * h) as usize];
let mut seen = HashSet::new();
let part2;
loop {
let (mdist, tool, x, y) = match pqu.pop() {
Some(val) => val,
None => panic!("Pqu empty!"),
};
let dist = -mdist;
if seen.contains(&(tool, x, y)) {
continue;
}
seen.insert((tool, x, y));
// println!("Expanding dist={} tool={} pos={:?}", dist, tool, (x, y));
if tool == 1 && x == target.0 as isize && y == target.1 as isize {
part2 = dist;
/* println!("Path:");
let mut at = (tool, x, y);
while at.0 != -1 {
println!(" tool={} pos=({}, {})", at.0, at.1, at.2);
at = parent[(w*h*at.0 + w*at.2 + at.1) as usize];
} */
break;
}
distmap[(w*h*tool + w*y + x) as usize] = dist;
for &pt in neighbours((x, y)).iter().filter(|&&pt| can_traverse(tool, pt)) {
if dist + 1 < distmap[(w*h*tool + w*pt.1 + pt.0) as usize] {
pqu.push((-(dist + 1), tool, pt.0, pt.1));
distmap[(w*h*tool + w*pt.1 + pt.0) as usize] = dist + 1;
// parent[(w*h*tool + w*pt.1 + pt.0) as usize] = (tool, x, y);
}
}
for t in 0..3 {
if t == tool { continue; }
if !can_traverse(t, (x, y)) { continue; }
if dist + 7 < distmap[(w*h*t + w*y + x) as usize] {
pqu.push((-(dist + 7), t, x, y));
distmap[(w*h*t + w*y + x) as usize] = dist + 7;
// parent[(w*h*t + w*y + x) as usize] = (tool, x, y);
}
}
}
Ok((part1.to_string(), part2.to_string()))
}
|
