jonas.tngl.sh
Advent of Code solutions in Rust
feat: day 6 of AoC 2025
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-2
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Cargo.lock
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Cargo.lock
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aoc_2025/Cargo.toml
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aoc_2025/Cargo.toml
+190
aoc_2025/src/day06.rs
+190
aoc_2025/src/day06.rs
···
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use aoc_companion::prelude::*;
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use itertools::Itertools as _;
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#[derive(Debug, PartialEq, Eq)]
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pub(crate) struct Door<'input> {
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operands: ndarray::Array2<&'input str>,
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operators: Vec<Op>,
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}
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impl<'input> Solution<'input> for Door<'input> {
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fn parse(input: &'input str) -> Result<Self> {
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let lines: Vec<_> = input.lines().collect();
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let Some((operator_line, operand_lines)) = lines.split_last() else {
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anyhow::bail!("homework is empty");
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};
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let column_offsets: Vec<usize> = operator_line
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.as_bytes()
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.iter()
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.positions(|b| *b != b' ')
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.collect();
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let operators = operator_line
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.split_ascii_whitespace()
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.map(|op| match op {
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"+" => Ok(Op::Add),
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"*" => Ok(Op::Mul),
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_ => Err(anyhow::anyhow!("invalid operator: {op:?}")),
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})
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.try_collect()?;
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let operands = operand_lines
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.iter()
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.flat_map(|line| {
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column_offsets
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.iter()
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.tuple_windows()
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.map(|(&a, &b)| &line[a..(b - 1)])
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.chain(std::iter::once(&line[*column_offsets.last().unwrap()..]))
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})
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.collect();
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Ok(Door {
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operands: ndarray::Array2::from_shape_vec(
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(operand_lines.len(), column_offsets.len()),
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operands,
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)?,
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operators,
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})
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}
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fn part1(&self) -> Result<u64> {
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Ok(self.to_human_math()?.solutions().iter().sum())
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}
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fn part2(&self) -> Result<u64> {
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Ok(self.to_cephalopod_math()?.solutions().iter().sum())
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}
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}
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impl Door<'_> {
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fn to_human_math(&self) -> Result<Homework> {
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let operands = self
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.operands
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.columns()
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.into_iter()
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.map(|col| col.iter().map(|s| s.trim().parse()).try_collect())
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.try_collect()?;
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Ok(Homework {
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operands,
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operators: self.operators.clone(),
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})
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}
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fn to_cephalopod_math(&self) -> Result<Homework> {
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let operands = self
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.operands
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.columns()
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.into_iter()
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.rev()
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.map(|col| {
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let width = col.get(0).map(|s| s.len()).unwrap_or_default();
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(0..width)
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.rev()
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.map(|i| {
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col.iter()
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.map(|s| {
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s.as_bytes()
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.get(i)
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.ok_or_else(|| anyhow::anyhow!("uneven column width"))
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})
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.filter_ok(|b| b.is_ascii_digit())
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.try_fold(0, |acc, b| -> Result<u64> {
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Ok(acc * 10 + u64::from(b? - b'0'))
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})
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})
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.try_collect()
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})
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.try_collect()?;
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Ok(Homework {
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operands,
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operators: self.operators.iter().cloned().rev().collect(),
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})
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}
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}
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#[derive(Debug, Clone, Copy, PartialEq, Eq)]
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enum Op {
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Add,
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Mul,
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}
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impl Op {
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fn neutral_element(&self) -> u64 {
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match self {
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Op::Add => 0,
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Op::Mul => 1,
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}
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}
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}
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struct Homework {
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operands: Vec<Vec<u64>>,
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operators: Vec<Op>,
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}
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impl Homework {
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fn solutions(&self) -> Vec<u64> {
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self.operands
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.iter()
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.zip(self.operators.iter())
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.map(|(col, op)| {
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col.iter().fold(
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op.neutral_element(),
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match op {
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Op::Add => std::ops::Add::add,
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Op::Mul => std::ops::Mul::mul,
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},
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)
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})
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.collect()
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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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const EXAMPLE_INPUT: &str = "\
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123 328 51 64
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45 64 387 23
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6 98 215 314
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* + * + ";
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#[test]
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fn parse_example_input() {
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assert_eq!(
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Door::parse(EXAMPLE_INPUT).unwrap(),
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Door {
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operands: ndarray::array![
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["123", "328", " 51", "64 "],
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[" 45", "64 ", "387", "23 "],
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[" 6", "98 ", "215", "314"],
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],
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operators: vec![Op::Mul, Op::Add, Op::Mul, Op::Add,]
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}
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)
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}
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#[test]
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fn example_human_solutions() {
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assert_eq!(
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Door::parse(EXAMPLE_INPUT)
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.unwrap()
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.to_human_math()
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.unwrap()
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.solutions(),
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[33210, 490, 4243455, 401]
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);
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}
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#[test]
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fn example_cephalopod_solutions() {
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assert_eq!(
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Door::parse(EXAMPLE_INPUT)
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.unwrap()
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.to_cephalopod_math()
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.unwrap()
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.solutions(),
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[1058, 3253600, 625, 8544]
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);
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}
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}
+2
-2
aoc_2025/src/main.rs
+2
-2
aoc_2025/src/main.rs
···
5
5
mod day03;
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6
mod day04;
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mod day05;
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-
// mod day06;
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mod day06;
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// mod day07;
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// mod day08;
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// mod day09;
···
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door!(2025-12-03 ~> day03),
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door!(2025-12-04 ~> day04),
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door!(2025-12-05 ~> day05),
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-
// door!(2025-12-06 ~> day06),
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door!(2025-12-06 ~> day06),
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// door!(2025-12-07 ~> day07),
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// door!(2025-12-08 ~> day08),
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// door!(2025-12-09 ~> day09),