jonas.tngl.sh
Advent of Code solutions in Rust
feat: part 2 of day 13 of AoC 2020
+138
+1
Cargo.lock
+1
Cargo.lock
+1
aoc_2020/Cargo.toml
+1
aoc_2020/Cargo.toml
+134
aoc_2020/src/day13.rs
+134
aoc_2020/src/day13.rs
···
27
27
earliest_departure(self.arrival_time, &self.bus_schedule)
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.ok_or_else(|| anyhow!("no buses scheduled"))
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}
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+
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+
fn part2(&self) -> Result<i128> {
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earliest_alignment(&self.bus_schedule).ok_or_else(|| anyhow!("no buses scheduled"))
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+
}
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34
}
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35
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enum BusLine {
···
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.map(|min_id| min_id * (min_id - arrival % min_id))
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}
67
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+
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
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struct Orbit {
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period: i128,
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+
phase: i128,
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+
}
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+
78
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fn combine_orbits(a: Orbit, b: Orbit) -> Orbit {
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use num_integer::ExtendedGcd;
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use num_integer::Integer as _;
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let (ExtendedGcd { gcd, x, y: _ }, lcm) = i128::extended_gcd_lcm(&a.period, &b.period);
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let (z, 0) = (a.phase - b.phase).div_rem(&gcd) else {
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panic!("orbits {a:?} and {b:?} never align");
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};
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Orbit {
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period: lcm,
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phase: (-z * x * a.period + a.phase).rem_euclid(lcm),
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}
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}
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+
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fn earliest_alignment(schedule: &[BusLine]) -> Option<i128> {
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schedule
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.iter()
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.enumerate()
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.filter_map(|(idx, bus)| {
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Some(Orbit {
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period: bus.id()? as i128,
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phase: idx as i128,
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+
})
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})
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.reduce(combine_orbits)
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.map(|o| (-o.phase).rem_euclid(o.period))
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}
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+
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#[cfg(test)]
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mod tests {
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use super::*;
···
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123
assert_eq!(
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earliest_departure(EXAMPLE_ARRIVAL, &EXAMPLE_SCHEDULE),
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Some(295)
126
+
);
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+
}
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+
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#[test]
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fn combine_orbits_incrementally() {
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+
assert_eq!(
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combine_orbits(
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+
Orbit {
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+
period: 3,
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+
phase: 0
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+
},
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+
Orbit {
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+
period: 4,
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+
phase: 1
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}
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),
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+
Orbit {
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+
period: 12,
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+
phase: 9 // = (-3) % 12
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}
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+
);
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+
assert_eq!(
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combine_orbits(
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+
Orbit {
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+
period: 12,
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+
phase: 9
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+
},
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+
Orbit {
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+
period: 5,
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+
phase: 3
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+
}
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),
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Orbit {
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+
period: 60,
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+
phase: 33 // = (-27) % 60
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}
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);
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+
}
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+
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+
#[test]
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fn find_earliest_alignment() {
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+
assert_eq!(
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earliest_alignment(&[
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+
BusLine::BusId(3),
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+
BusLine::BusId(4),
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+
BusLine::Omission,
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+
BusLine::BusId(5),
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+
]),
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+
Some(27)
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+
);
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+
assert_eq!(earliest_alignment(&EXAMPLE_SCHEDULE), Some(1068781));
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+
assert_eq!(
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earliest_alignment(&[
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+
BusLine::BusId(17),
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+
BusLine::Omission,
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+
BusLine::BusId(13),
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+
BusLine::BusId(19),
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+
]),
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+
Some(3417)
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+
);
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+
assert_eq!(
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earliest_alignment(&[
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+
BusLine::BusId(67),
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+
BusLine::BusId(7),
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+
BusLine::BusId(59),
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+
BusLine::BusId(61),
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+
]),
193
+
Some(754018)
194
+
);
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+
assert_eq!(
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+
earliest_alignment(&[
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+
BusLine::BusId(67),
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+
BusLine::Omission,
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+
BusLine::BusId(7),
200
+
BusLine::BusId(59),
201
+
BusLine::BusId(61),
202
+
]),
203
+
Some(779210)
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+
);
205
+
assert_eq!(
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+
earliest_alignment(&[
207
+
BusLine::BusId(67),
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+
BusLine::BusId(7),
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+
BusLine::Omission,
210
+
BusLine::BusId(59),
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+
BusLine::BusId(61),
212
+
]),
213
+
Some(1261476)
214
+
);
215
+
assert_eq!(
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+
earliest_alignment(&[
217
+
BusLine::BusId(1789),
218
+
BusLine::BusId(37),
219
+
BusLine::BusId(47),
220
+
BusLine::BusId(1889),
221
+
]),
222
+
Some(1202161486)
89
223
);
90
224
}
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225
}
+2
aoc_companion/src/door.rs
+2
aoc_companion/src/door.rs