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use std::collections::VecDeque;
use md5;
fn solve_puzzle(passwd: &str) -> Vec<String> {
let mut paths = Vec::new();
// Breadth-first search of all possible paths
let start = (String::new(), (0, 0));
let mut queue = VecDeque::from([start]);
loop {
let pp = queue.pop_front();
// All paths have finished or got stuck at locked doors
if pp.is_none() {
break;
}
// Did we successfully reach the bottom-right corner?
let (path, pos) = pp.unwrap();
if pos == (3, 3) {
paths.push(path.clone());
continue;
}
// Doors open based on MD5 hash of `passw' + `path'
let data = format!("{}{}", passwd, path);
let hash: Vec<char> = format!("{:x}", md5::compute(data)).chars().collect();
// Which doors are open, i.e. what are the valid next moves?
let mut options = Vec::new();
let unlock = ['b', 'c', 'd', 'e', 'f'];
if unlock.contains(&hash[0]) && pos.1 > 0 {
options.push((format!("{}U", path), (pos.0, pos.1 - 1)));
}
if unlock.contains(&hash[1]) && pos.1 < 3 {
options.push((format!("{}D", path), (pos.0, pos.1 + 1)));
}
if unlock.contains(&hash[2]) && pos.0 > 0 {
options.push((format!("{}L", path), (pos.0 - 1, pos.1)));
}
if unlock.contains(&hash[3]) && pos.0 < 3 {
options.push((format!("{}R", path), (pos.0 + 1, pos.1)));
}
// This is a breadth-first search, but because `path' is encoded
// into the state, we don't need to check that nodes are unexplored
for (npath, npos) in options {
queue.push_back((npath, npos));
}
}
paths
}
fn main() {
// My personal puzzle input
let input = "edjrjqaa";
let paths = solve_puzzle(input);
// Part 1 gives "DUDRDLRRRD" for me
println!("Part 1 solution: {}", paths.first().unwrap());
// Part 2 gives 502 for me
println!("Part 2 solution: {}", paths.last().unwrap().len());
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn part1_example1() {
let passwd = "ihgpwlah";
assert_eq!(solve_puzzle(passwd).first().unwrap(), "DDRRRD");
}
#[test]
fn part2_example1() {
let passwd = "ihgpwlah";
assert_eq!(solve_puzzle(passwd).last().unwrap().len(), 370);
}
#[test]
fn part1_example2() {
let passwd = "kglvqrro";
assert_eq!(solve_puzzle(passwd).first().unwrap(), "DDUDRLRRUDRD");
}
#[test]
fn part2_example2() {
let passwd = "kglvqrro";
assert_eq!(solve_puzzle(passwd).last().unwrap().len(), 492);
}
#[test]
fn part1_example3() {
let passwd = "ulqzkmiv";
assert_eq!(
solve_puzzle(passwd).first().unwrap(),
"DRURDRUDDLLDLUURRDULRLDUUDDDRR"
);
}
#[test]
fn part2_example3() {
let passwd = "ulqzkmiv";
assert_eq!(solve_puzzle(passwd).last().unwrap().len(), 830);
}
}
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