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| 1 | +//! [Day 24: Crossed Wires](https://adventofcode.com/2024/day/24) |
| 2 | +
|
| 3 | +// Circuit diagrams are copied from: |
| 4 | +// https://www.researchgate.net/publication/349727409_PyQUBO_Python_Library_for_Mapping_Combinatorial_Optimization_Problems_to_QUBO_Form |
| 5 | +// |
| 6 | +// @unknown{unknown, |
| 7 | +// author = {Zaman, Mashiyat and Tanahashi, Kotaro and Tanaka, Shu}, |
| 8 | +// year = {2021}, |
| 9 | +// month = {03}, |
| 10 | +// pages = {}, |
| 11 | +// title = {PyQUBO: Python Library for Mapping Combinatorial Optimization Problems to QUBO Form}, |
| 12 | +// doi = {10.48550/arXiv.2103.01708} |
| 13 | +// } |
| 14 | +// |
| 15 | + |
| 16 | +use std::collections::{HashMap, HashSet}; |
| 17 | + |
| 18 | +#[derive(Eq, PartialEq, Hash, Clone, Debug)] |
| 19 | +enum Role { |
| 20 | + CarryOut, // the Cout wire |
| 21 | + IntXorXor, // intermediate wire between the two XOR gates |
| 22 | + ABAndGate, // intermediate wires between AB and the (bottom) AND gate |
| 23 | + AndGateWires, // wiring of the AND gates |
| 24 | + SumOut, // the S wire |
| 25 | +} |
| 26 | + |
| 27 | +#[derive(Eq, PartialEq, Hash, Clone)] |
| 28 | +enum Operation { |
| 29 | + And, |
| 30 | + Or, |
| 31 | + Xor, |
| 32 | +} |
| 33 | + |
| 34 | +impl Operation { |
| 35 | + fn from(s: &str) -> Self { |
| 36 | + match s { |
| 37 | + "AND" => Self::And, |
| 38 | + "OR" => Self::Or, |
| 39 | + "XOR" => Self::Xor, |
| 40 | + _ => panic!("unknown op {s}"), |
| 41 | + } |
| 42 | + } |
| 43 | + |
| 44 | + const fn eval(&self, a: u8, b: u8) -> u8 { |
| 45 | + match self { |
| 46 | + Self::And => a & b, |
| 47 | + Self::Or => a | b, |
| 48 | + Self::Xor => a ^ b, |
| 49 | + } |
| 50 | + } |
| 51 | +} |
| 52 | + |
| 53 | +#[derive(Eq, PartialEq, Hash, Clone)] |
| 54 | +struct Gate { |
| 55 | + a: String, // input wire |
| 56 | + b: String, // input wire |
| 57 | + op: Operation, // type of gate |
| 58 | + r: String, // output wire |
| 59 | +} |
| 60 | + |
| 61 | +fn is_role(set: &HashSet<Role>, f: &Role) -> bool { |
| 62 | + set.len() == 1 && (set.iter().next().unwrap() == f) |
| 63 | +} |
| 64 | + |
| 65 | +fn is_roles(set: &HashSet<Role>, f1: &Role, f2: &Role) -> bool { |
| 66 | + if set.len() != 2 { |
| 67 | + return false; |
| 68 | + } |
| 69 | + |
| 70 | + let roles: Vec<_> = set.iter().collect(); |
| 71 | + (roles[0] == f1 && roles[1] == f2) || (roles[0] == f2 && roles[1] == f1) |
| 72 | +} |
| 73 | + |
| 74 | +struct Puzzle { |
| 75 | + // data: String, |
| 76 | + wires: HashMap<String, u8>, |
| 77 | + gates: Vec<Gate>, |
| 78 | +} |
| 79 | + |
| 80 | +impl Puzzle { |
| 81 | + fn new() -> Self { |
| 82 | + Self { |
| 83 | + wires: HashMap::new(), |
| 84 | + gates: Vec::new(), |
| 85 | + } |
| 86 | + } |
| 87 | + |
| 88 | + /// Get the puzzle input. |
| 89 | + fn configure(&mut self, path: &str) { |
| 90 | + let data = std::fs::read_to_string(path).unwrap_or_else(|_| { |
| 91 | + eprintln!("cannot read input file {path}"); |
| 92 | + std::process::exit(1); |
| 93 | + }); |
| 94 | + |
| 95 | + for line in data.lines() { |
| 96 | + if line.contains(": ") { |
| 97 | + let (wire, value) = line.split_once(": ").unwrap(); |
| 98 | + self.wires.insert(wire.to_string(), value.parse().unwrap()); |
| 99 | + } |
| 100 | + if line.contains(" -> ") { |
| 101 | + let v = line.split_ascii_whitespace().collect::<Vec<_>>(); |
| 102 | + |
| 103 | + let gate = Gate { |
| 104 | + a: v[0].to_string(), |
| 105 | + op: Operation::from(v[1]), |
| 106 | + b: v[2].to_string(), |
| 107 | + r: v[4].to_string(), |
| 108 | + }; |
| 109 | + |
| 110 | + self.gates.push(gate); |
| 111 | + } |
| 112 | + } |
| 113 | + } |
| 114 | + |
| 115 | + /// Solve part one. |
| 116 | + fn part1(&self) -> u64 { |
| 117 | + let mut waiting_gates = self.gates.iter().collect::<Vec<_>>(); |
| 118 | + let mut wires = self.wires.clone(); |
| 119 | + |
| 120 | + while !waiting_gates.is_empty() { |
| 121 | + let mut next_waiting = Vec::new(); |
| 122 | + |
| 123 | + for gate in &waiting_gates { |
| 124 | + if let Some(&a) = wires.get(&gate.a) { |
| 125 | + if let Some(&b) = wires.get(&gate.b) { |
| 126 | + let r = gate.op.eval(a, b); |
| 127 | + *wires.entry(gate.r.to_string()).or_default() = r; |
| 128 | + continue; |
| 129 | + } |
| 130 | + } |
| 131 | + |
| 132 | + next_waiting.push(*gate); |
| 133 | + } |
| 134 | + |
| 135 | + waiting_gates = next_waiting; |
| 136 | + } |
| 137 | + |
| 138 | + wires |
| 139 | + .iter() |
| 140 | + .filter(|(r, &v)| r.starts_with('z') && v == 1) |
| 141 | + .fold(0_u64, |acc, (r, _)| { |
| 142 | + acc | (1 << r[1..].parse::<u64>().unwrap()) |
| 143 | + }) |
| 144 | + } |
| 145 | + |
| 146 | + /// Solve part two. |
| 147 | + fn part2(&self) -> String { |
| 148 | + let mut input_types: HashMap<&str, HashSet<Role>> = HashMap::new(); |
| 149 | + let mut result_types: HashMap<&str, HashSet<Role>> = HashMap::new(); |
| 150 | + |
| 151 | + // analyse the role of each gate |
| 152 | + |
| 153 | + for gate in &self.gates { |
| 154 | + if gate.a == "x00" && gate.b == "y00" || gate.b == "x00" && gate.a == "y00" { |
| 155 | + // ignore first half adder |
| 156 | + continue; |
| 157 | + } |
| 158 | + |
| 159 | + let mut add_result_role = |
| 160 | + |r: &Role| result_types.entry(&gate.r).or_default().insert(r.clone()); |
| 161 | + |
| 162 | + // full adder |
| 163 | + if (gate.a.starts_with('x') && gate.b.starts_with('y')) |
| 164 | + || (gate.a.starts_with('y') && gate.b.starts_with('x')) |
| 165 | + { |
| 166 | + add_result_role(match gate.op { |
| 167 | + Operation::Xor => &Role::IntXorXor, // xy connected to the 1st XOR gate: output is the wire between the both XOR |
| 168 | + Operation::And => &Role::ABAndGate, // xy wired to a AND gate |
| 169 | + Operation::Or => panic!("OR gate should be wired to x/y"), |
| 170 | + }); |
| 171 | + } else { |
| 172 | + let role = match gate.op { |
| 173 | + Operation::Xor => &Role::SumOut, // actually the 2nd XOR gate |
| 174 | + Operation::And => &Role::AndGateWires, // connections of AND gates |
| 175 | + Operation::Or => &Role::CarryOut, // the only one OR gate is wired to Cout |
| 176 | + }; |
| 177 | + |
| 178 | + input_types.entry(&gate.a).or_default().insert(role.clone()); |
| 179 | + input_types.entry(&gate.b).or_default().insert(role.clone()); |
| 180 | + add_result_role(role); |
| 181 | + } |
| 182 | + } |
| 183 | + |
| 184 | + // branch all logical adders |
| 185 | + |
| 186 | + let last_z_wire = result_types |
| 187 | + .keys() |
| 188 | + .filter(|wire| wire.starts_with('z')) |
| 189 | + .max() |
| 190 | + .unwrap(); |
| 191 | + |
| 192 | + let mut bad_wires: Vec<&str> = Vec::new(); |
| 193 | + |
| 194 | + for wire in result_types.keys() { |
| 195 | + let inp = &input_types.entry(wire).or_default(); |
| 196 | + let res = &result_types[wire]; |
| 197 | + |
| 198 | + if wire == last_z_wire && is_role(res, &Role::CarryOut) { |
| 199 | + // ok, last wire/bit of the result register should be wired to CarryOut |
| 200 | + continue; |
| 201 | + } |
| 202 | + |
| 203 | + if inp.is_empty() && wire.starts_with('z') && is_role(res, &Role::SumOut) { |
| 204 | + // ok, other z wires are Sum outputs |
| 205 | + continue; |
| 206 | + } |
| 207 | + |
| 208 | + if is_role(inp, &Role::CarryOut) |
| 209 | + && (is_role(res, &Role::AndGateWires) || is_role(res, &Role::ABAndGate)) |
| 210 | + { |
| 211 | + // ok: CarryOut should be wired to 2nd XOR or a AND gate |
| 212 | + continue; |
| 213 | + } |
| 214 | + |
| 215 | + if is_roles(inp, &Role::SumOut, &Role::AndGateWires) |
| 216 | + && (is_role(res, &Role::CarryOut) || is_role(res, &Role::IntXorXor)) |
| 217 | + { |
| 218 | + // ok: Cin and Sum should be wired to Cout or |
| 219 | + continue; |
| 220 | + } |
| 221 | + |
| 222 | + #[cfg(debug_assertions)] |
| 223 | + eprintln!("❌ {wire} : {inp:?} → {res:?}"); |
| 224 | + |
| 225 | + // ⚠️ swapped wire pairs are not determined, |
| 226 | + // ⚠️ just the eight incorrectly wired |
| 227 | + |
| 228 | + bad_wires.push(wire); |
| 229 | + } |
| 230 | + |
| 231 | + bad_wires.sort_unstable(); |
| 232 | + bad_wires.join(",") |
| 233 | + } |
| 234 | +} |
| 235 | + |
| 236 | +fn main() { |
| 237 | + let args = aoc::parse_args(); |
| 238 | + let mut puzzle = Puzzle::new(); |
| 239 | + puzzle.configure(args.path.as_str()); |
| 240 | + println!("{}", puzzle.part1()); |
| 241 | + println!("{}", puzzle.part2()); |
| 242 | +} |
| 243 | + |
| 244 | +/// Test from puzzle input |
| 245 | +#[cfg(test)] |
| 246 | +mod test { |
| 247 | + use super::*; |
| 248 | + |
| 249 | + #[test] |
| 250 | + fn test_part1() { |
| 251 | + let mut puzzle = Puzzle::new(); |
| 252 | + puzzle.configure("sample_1.txt"); |
| 253 | + assert_eq!(puzzle.part1(), 4); |
| 254 | + } |
| 255 | + |
| 256 | + #[test] |
| 257 | + fn test_part2() { |
| 258 | + let mut puzzle = Puzzle::new(); |
| 259 | + puzzle.configure("sample_2.txt"); |
| 260 | + assert_eq!(puzzle.part1(), 2024); |
| 261 | + } |
| 262 | +} |
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