2020: day10: part 2
This commit is contained in:
parent
2726134d7d
commit
2381f61118
|
@ -1,3 +1,4 @@
|
|||
use std::collections::HashMap;
|
||||
use std::fmt::Write;
|
||||
|
||||
use aoc::err;
|
||||
|
@ -8,6 +9,7 @@ pub fn run() -> aoc::Result<String> {
|
|||
let mut res = String::with_capacity(128);
|
||||
|
||||
writeln!(res, "part 1: {}", part1(INPUT)?)?;
|
||||
writeln!(res, "part 2: {}", part2(INPUT)?)?;
|
||||
|
||||
Ok(res)
|
||||
}
|
||||
|
@ -45,6 +47,65 @@ fn part1(input: &str) -> aoc::Result<usize> {
|
|||
Ok(differences[1] * differences[3])
|
||||
}
|
||||
|
||||
fn find_possibilities(jolts: &[u64], possibilities: &mut HashMap<u64, usize>) -> usize {
|
||||
if let Some(&count) = possibilities.get(&jolts[0]) {
|
||||
return count;
|
||||
}
|
||||
|
||||
if jolts.len() == 1 {
|
||||
return 1;
|
||||
}
|
||||
|
||||
let curr = jolts[0];
|
||||
|
||||
let possibilities_from_here = jolts
|
||||
.iter()
|
||||
.copied()
|
||||
// we need the index to step in the jolt slice
|
||||
.enumerate()
|
||||
// skip the current adapter one
|
||||
.skip(1)
|
||||
// its 3 successors can possibly be removed
|
||||
.take(3)
|
||||
// remove adapter if the jolt difference is too high
|
||||
.filter(|(_, jolt)| jolt - curr <= 3)
|
||||
// count each possible next adapter and all its possibilities
|
||||
.map(|(idx, _)| find_possibilities(&jolts[idx..], possibilities))
|
||||
.sum();
|
||||
|
||||
possibilities.insert(curr, possibilities_from_here);
|
||||
|
||||
possibilities_from_here
|
||||
}
|
||||
|
||||
fn part2(input: &str) -> aoc::Result<usize> {
|
||||
let mut jolts = input
|
||||
.lines()
|
||||
.map(|line| {
|
||||
line.parse()
|
||||
.map_err(|e| err!("couldn't parse joltage: {}", e))
|
||||
})
|
||||
.collect::<aoc::Result<Vec<u64>>>()?;
|
||||
|
||||
if jolts.is_empty() {
|
||||
return Err(err!("input was empty!"));
|
||||
}
|
||||
|
||||
// charging outlet can be added
|
||||
jolts.insert(0, 0);
|
||||
|
||||
jolts.sort_unstable();
|
||||
|
||||
// device is rated for max adapter + 3 jolts
|
||||
let max_adapter = jolts[jolts.len() - 1];
|
||||
let device_rating = max_adapter + 3;
|
||||
jolts.push(device_rating);
|
||||
|
||||
let mut possibilities = HashMap::new();
|
||||
|
||||
Ok(find_possibilities(&jolts, &mut possibilities))
|
||||
}
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use super::*;
|
||||
|
@ -62,4 +123,15 @@ mod tests {
|
|||
fn part1_real() {
|
||||
assert_eq!(part1(INPUT).unwrap(), 2112);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn part2_provided() {
|
||||
assert_eq!(part2(PROVIDED1).unwrap(), 8);
|
||||
assert_eq!(part2(PROVIDED2).unwrap(), 19208);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn part2_real() {
|
||||
assert_eq!(part2(INPUT).unwrap(), 3022415986688);
|
||||
}
|
||||
}
|
||||
|
|
Loading…
Reference in a new issue