3 files changed, 140 insertions, 1 deletions
diff --git a/2022/rust/Cargo.toml b/2022/rust/Cargo.toml
index b7ab11d..e127354 100644
--- a/2022/rust/Cargo.toml
+++ b/2022/rust/Cargo.toml
@@ -4,7 +4,7 @@ members = [
      "day02",
      "day03",
      "day04",
-#     "day05",
+     "day05",
 #     "day06",
 #     "day07",
 #     "day08",
diff --git a/2022/rust/day05/Cargo.toml b/2022/rust/day05/Cargo.toml
new file mode 100644
index 0000000..ee89cea
--- /dev/null
+++ b/2022/rust/day05/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day05"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+aoc = { path = "../../../common/rust/aoc" }
+anyhow = "1.0"
+regex = "1.7.0"
diff --git a/2022/rust/day05/src/main.rs b/2022/rust/day05/src/main.rs
new file mode 100644
index 0000000..b50114f
--- /dev/null
+++ b/2022/rust/day05/src/main.rs
@@ -0,0 +1,130 @@
+use {
+    anyhow::{
+        anyhow,
+        Context,
+        Result,
+    },
+    regex::Regex,
+    std::{
+        collections::HashMap,
+        env::args,
+        path::Path,
+    },
+};
+
+type Stack = Vec<char>;
+type Stacks = HashMap<usize, Stack>;
+
+#[derive(Debug)]
+struct Rearrangment {
+    count: usize,
+    from: usize,
+    to: usize,
+}
+
+impl Rearrangment {
+    fn new(count: usize, from: usize, to: usize) -> Self {
+        Self {
+            count,
+            from,
+            to,
+        }
+    }
+}
+
+fn read_input<T: AsRef<Path>>(filename: T) -> Result<(Stacks, Vec<Rearrangment>)> {
+    let re = Regex::new(r"move (?P<count>[0-9]+) from (?P<from>[0-9]+) to (?P<to>[0-9]+)")?;
+
+    let content = std::fs::read_to_string(filename)?;
+    let (picture, lines) = content.split_once("\n\n").ok_or_else(|| anyhow!("Invalid input"))?;
+
+    let mut stacks = HashMap::new();
+    for layer in picture.split('\n') {
+        for (num, chunk) in layer.as_bytes().chunks(4).enumerate() {
+            let byte = chunk.get(1).ok_or_else(|| anyhow!("Could not parse picture."))?;
+            let ch = *byte as char;
+            if ('A'..='Z').contains(&ch) {
+                stacks.entry(num + 1).and_modify(|e: &mut Vec<char>| e.insert(0, ch))
+                    .or_insert_with(|| vec![ch]);
+            }
+        }
+    }
+
+    let rearrangements = lines.split('\n').filter(|line| !line.is_empty()).map(|line| {
+        let caps = re.captures(line).ok_or_else(|| anyhow!("Regex matching failed."))?;
+
+        match (caps.name("count"), caps.name("from"), caps.name("to")) {
+            (Some(count), Some(from), Some(to)) => Ok(Rearrangment::new(count.as_str().parse()?,
+                from.as_str().parse()?, to.as_str().parse()?)),
+            _ => Err(anyhow!("Failed to parse rearrangements.")),
+        }
+    }).collect::<Result<Vec<_>>>()?;
+
+    Ok((stacks, rearrangements))
+}
+
+fn part1(input_stacks: &Stacks, rearrangements: &[Rearrangment]) -> Result<String> {
+    let mut stacks = input_stacks.clone();
+    for rearrangement in rearrangements {
+        let count = rearrangement.count;
+        let from = rearrangement.from;
+        let to = rearrangement.to;
+        for _ in 0..count {
+            let source = stacks.get_mut(&from)
+                .ok_or_else(|| anyhow!("Missing stack {from}"))?;
+            if let Some(elem) = source.pop() {
+                let destination = stacks.get_mut(&to)
+                    .ok_or_else(|| anyhow!("Missing stack {to}"))?;
+                destination.push(elem);
+            }
+        }
+    }
+
+    let mut keys: Vec<_> = stacks.keys().cloned().collect();
+    keys.sort();
+
+    Ok(keys.iter().filter_map(|key| {
+        let stack = stacks.get_mut(key).unwrap_or_else(|| unreachable!());
+        stack.pop()
+    }).collect())
+}
+
+fn part2(input_stacks: &Stacks, rearrangements: &[Rearrangment]) -> Result<String> {
+    let mut stacks = input_stacks.clone();
+    for rearrangement in rearrangements {
+        let count = rearrangement.count;
+        let from = rearrangement.from;
+        let to = rearrangement.to;
+        let source = stacks.get_mut(&from)
+            .ok_or_else(|| anyhow!("Missing stack {from}"))?;
+
+        let mut elems = source.drain(source.len()-count..).collect();
+        let destination = stacks.get_mut(&to)
+            .ok_or_else(|| anyhow!("Missing stack {to}"))?;
+        destination.append(&mut elems);
+    }
+
+    let mut keys: Vec<_> = stacks.keys().cloned().collect();
+    keys.sort();
+
+    Ok(keys.iter().filter_map(|key| {
+        let stack = stacks.get_mut(key).unwrap_or_else(|| unreachable!());
+        stack.pop()
+    }).collect())
+}
+
+fn main() -> Result<()> {
+    let ( do_part_1, do_part_2 ) = aoc::do_parts();
+
+    let filename = args().nth(1).ok_or_else(|| anyhow!("Missing input filename"))?;
+    let (stacks, rearrangements) = read_input(filename).context("Could not read input")?;
+    if do_part_1 {
+        let solution = part1(&stacks, &rearrangements).context("No solution for part 1")?;
+        println!("Part1, solution found to be: {}", solution);
+    }
+    if do_part_2 {
+        let solution = part2(&stacks, &rearrangements).context("No solution for part 2")?;
+        println!("Part2, solution found to be: {}", solution);
+    }
+    Ok(())
+}