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Diffstat (limited to '2021/rust/day01/src/main.rs')
-rw-r--r-- | 2021/rust/day01/src/main.rs | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/2021/rust/day01/src/main.rs b/2021/rust/day01/src/main.rs new file mode 100644 index 0000000..a3a6e73 --- /dev/null +++ b/2021/rust/day01/src/main.rs @@ -0,0 +1,82 @@ +use { + anyhow::{ + anyhow, + Context, + Result, + }, + std::{ + env::args, + fs::File, + io::{ + BufRead, + BufReader, + }, + path::Path, + }, +}; + +fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<usize>> { + let reader = BufReader::new(File::open(filename)?); + + reader.lines().map( + |v| v?.parse().map_err(|err| anyhow!("Could not parse input: {}", err)) + ).collect() +} + +#[derive(PartialEq)] +enum Change { + NoPrevVal, + Increased, + Decreased, + Identical, +} + +fn count_increases(values: &[usize]) -> usize { + let changes: Vec<Change> = values.iter().scan(None, |state, val| { + let next = match state { + None => Change::NoPrevVal, + Some(prev) if val < prev => Change::Decreased, + Some(prev) if val > prev => Change::Increased, + Some(prev) if val == prev => Change::Identical, + Some(_) => unreachable!(), + }; + *state = Some(*val); + Some(next) + }).collect(); + + changes.iter().fold(0, |count, change| + if *change == Change::Increased { count + 1 } else { count } + ) +} + +fn part1(input: &[usize]) -> Result<usize> { + let count = count_increases(input); + + Ok(count) +} + +fn part2(input: &[usize]) -> Result<usize> { + let slidesums: Vec<_> = input.iter().zip(input[1..].iter()).zip(input[2..].iter()).map(|n| { + let ((first, second), third) = n; + first + second + third + }).collect(); + let count = count_increases(&slidesums); + + Ok(count) +} + +fn main() -> Result<()> { + let ( do_part_1, do_part_2 ) = aoc::do_parts(); + + let filename = args().nth(1).ok_or(anyhow!("Missing input filename"))?; + let input = read_input(filename).context("Could not read input")?; + if do_part_1 { + let solution = part1(&input).context("No solution for part 1")?; + println!("Part1, number of increases found to be: {}", solution); + } + if do_part_2 { + let solution = part2(&input).context("No solution for part 2")?; + println!("Part2, number of increases found to be: {}", solution); + } + Ok(()) +} |