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// Let the record show that I hated every second of solving this puzzle.
use std::fs;
#[derive(Copy, Clone, Debug)]
struct Bot {
lo: Option<usize>,
hi: Option<usize>,
}
impl Bot {
fn new() -> Self {
Self { lo: None, hi: None }
}
fn recv_chip(&mut self, val: usize) {
if self.lo.is_none() && self.hi.is_none() {
self.lo = Some(val);
} else if self.lo.is_some() && self.hi.is_none() {
let old_lo = self.lo.unwrap();
if old_lo < val {
self.hi = Some(val);
} else {
self.lo = Some(val);
self.hi = Some(old_lo);
}
} else if self.lo.is_none() && self.hi.is_some() {
let old_hi = self.hi.unwrap();
if old_hi > val {
self.lo = Some(val);
} else {
self.lo = Some(old_hi);
self.hi = Some(val);
}
} else if self.lo.is_some() && self.hi.is_some() {
// If both slots are occupied, we can't accept any more
}
}
fn give_chip_lo(&mut self) -> Option<usize> {
let result = self.lo;
if result.is_some() {
self.lo = None;
}
result
}
fn give_chip_hi(&mut self) -> Option<usize> {
let result = self.hi;
if result.is_some() {
self.hi = None;
}
result
}
fn num_chips(&self) -> usize {
let mut result = 0;
if self.lo.is_some() {
result += 1;
}
if self.hi.is_some() {
result += 1;
}
result
}
}
fn solve_puzzle(lines: &Vec<&str>, target: (usize, usize)) -> (usize, usize) {
let mut bots: Vec<Bot> = [Bot::new()].repeat(300);
let mut bins: Vec<Option<usize>> = [None].repeat(300);
let mut part1 = None;
let mut part2 = None;
let mut ln = 0;
// Loop 50k times until a self-consistent state is reached
for _i in 0..50000 {
let words: Vec<&str> = lines[ln].split_ascii_whitespace().collect();
// Take chip from input bin
if words[0] == "value" {
let to: usize = words[5].parse().unwrap();
bots[to].recv_chip(words[1].parse().unwrap());
}
// Give chips to other bots or to output bins
if words[0] == "bot" {
let from: usize = words[1].parse().unwrap();
// Does the giver have two chips? If not, ignore this line (for now)
if bots[from].lo.is_some() && bots[from].hi.is_some() {
// Bot/bin indices to give chips to
let lo_to: usize = words[6].parse().unwrap();
let hi_to: usize = words[11].parse().unwrap();
// Can the destination accept our chips?
let lo_avail =
(words[5] == "bot" && bots[lo_to].num_chips() < 2) || words[5] == "output";
let hi_avail =
(words[10] == "bot" && bots[hi_to].num_chips() < 2) || words[10] == "output";
if lo_avail && hi_avail {
// Give the low chip
let lo = bots[from].give_chip_lo().unwrap();
if words[5] == "bot" {
bots[lo_to].recv_chip(lo);
} else if words[5] == "output" {
bins[lo_to] = Some(lo); // overwrite
}
// Give the high chip
let hi = bots[from].give_chip_hi().unwrap();
if words[10] == "bot" {
bots[hi_to].recv_chip(hi);
} else if words[10] == "output" {
bins[hi_to] = Some(hi); // overwrite
}
}
}
}
// Which bot ends up comparing the target-valued chips?
for j in 0..bots.len() {
if bots[j].lo.is_some() && bots[j].lo.unwrap() == target.0 {
if bots[j].hi.is_some() && bots[j].hi.unwrap() == target.1 {
part1 = Some(j);
}
}
}
// What is the product of the chips that end up in output bins 0, 1 and 2?
if bins[0].is_some() && bins[1].is_some() && bins[2].is_some() {
part2 = Some(bins[0].unwrap() * bins[1].unwrap() * bins[2].unwrap());
}
ln = (ln + 1) % lines.len();
}
(part1.unwrap(), part2.unwrap())
}
fn main() {
// Read instructions from input text file
let input = fs::read_to_string("input.txt").unwrap();
let lines = input.lines().collect();
let (part1, part2) = solve_puzzle(&lines, (17, 61));
// Part 1 gives 101 for me
println!("Part 1 solution: {}", part1);
// Part 2 gives 37789 for me
println!("Part 2 solution: {}", part2);
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn part1_example1() {
let lines = vec![
"value 5 goes to bot 2",
"bot 2 gives low to bot 1 and high to bot 0",
"value 3 goes to bot 1",
"bot 1 gives low to output 1 and high to bot 0",
"bot 0 gives low to output 2 and high to output 0",
"value 2 goes to bot 2",
];
assert_eq!(solve_puzzle(&lines, (2, 5)), (2, 30));
}
}
|
