2 files changed, 91 insertions, 0 deletions
diff --git a/2021/rust/day01/Cargo.toml b/2021/rust/day01/Cargo.toml
new file mode 100644
index 0000000..afa6985
--- /dev/null
+++ b/2021/rust/day01/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day01"
+version = "0.1.0"
+authors = ["cos <cos>"]
+edition = "2021"
+
+[dependencies]
+aoc = { path = "../../../common/rust/aoc" }
+anyhow = "1.0"
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(())
+}