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use std::collections::HashMap;
use std::collections::BinaryHeap;
use std::cmp::Ordering;
fn main() {
let input = advent::read_lines(15);
println!("15a: {}", lowest_risk(&input));
println!("15b: {}", lowest_risk_large(&input));
}
#[derive(PartialEq,Eq,Hash,Clone,Copy,Debug)]
struct Position {
x: isize,
y: isize,
}
#[derive(PartialEq,Eq,Clone,Copy)]
struct State {
pos: Position,
cost: isize,
}
/* comparator for priority queue */
impl Ord for State {
fn cmp(&self, other: &Self) -> Ordering {
other.cost.cmp(&self.cost)
}
}
impl PartialOrd for State {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}
/* Dijkstra implementation from https://doc.rust-lang.org/std/collections/binary_heap/index.html */
fn dijkstra(map: &HashMap<Position, isize>, from: &Position, to: &Position) -> isize {
let mut dist = HashMap::new();
let mut heap = BinaryHeap::new();
for pos in map.keys() {
if pos != from {
dist.insert(*pos, isize::MAX);
}
}
dist.insert(*from, 0);
heap.push(State { cost: 0, pos: *from });
while let Some(State { cost, pos }) = heap.pop() {
if pos == *to { return cost; }
if cost > dist[&pos] { continue; }
for (x, y) in [(1, 0), (0, 1), (0, -1), (-1, 0)] {
let neigh_pos = Position { x: pos.x + x, y: pos.y + y };
if !map.contains_key(&neigh_pos) {
continue;
}
let neigh = State { cost: cost + *map.get(&pos).unwrap(), pos: neigh_pos };
if neigh.cost < dist[&neigh.pos] {
heap.push(neigh);
dist.insert(neigh.pos, neigh.cost);
}
}
}
panic!("no path found");
}
fn parse_map<T: AsRef<str>>(input: &[T]) -> HashMap<Position, isize> {
let mut map = HashMap::new();
for (y, line) in input.iter().enumerate() {
for (x, c) in line.as_ref().chars().enumerate() {
let risk = c.to_digit(10).unwrap() as isize;
map.insert(Position { x: x as isize, y: y as isize }, risk);
}
}
map
}
fn lowest_risk<T: AsRef<str>>(input: &[T]) -> isize {
let map = parse_map(input);
let start = Position { x: 0, y: 0 };
let end = *map.keys().max_by_key(|&pos| pos.x + pos.y).unwrap();
dijkstra(&map, &end, &start)
}
fn lowest_risk_large<T: AsRef<str>>(input: &[T]) -> isize {
let map = parse_map(input);
let start = Position { x: 0, y: 0 };
let end = *map.keys().max_by_key(|&pos| pos.x + pos.y).unwrap();
let length = end.x + 1;
let mut large_map = HashMap::new();
for x in 0 .. 5 {
for y in 0 .. 5 {
for (pos, risk) in &map {
let pos = Position {
x: pos.x + x * length,
y: pos.y + y * length,
};
let risk = ((risk - 1 + x + y) % 9) + 1;
large_map.insert(pos, risk);
}
}
}
let end = *large_map.keys().max_by_key(|&pos| pos.x + pos.y).unwrap();
dijkstra(&large_map, &end, &start)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"1163751742",
"1381373672",
"2136511328",
"3694931569",
"7463417111",
"1319128137",
"1359912421",
"3125421639",
"1293138521",
"2311944581",
];
assert_eq!(lowest_risk(&input), 40);
assert_eq!(lowest_risk_large(&input), 315);
}
}
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