1 files changed, 145 insertions, 0 deletions
diff --git a/2022/src/day05.rs b/2022/src/day05.rs
new file mode 100644
index 0000000..f45cd0a
--- /dev/null
+++ b/2022/src/day05.rs
@@ -0,0 +1,145 @@
+//! Day 5: Supply Stacks
+
+extern crate bumpalo;
+
+mod utils;
+
+use bumpalo::Bump;
+use std::cell::Cell;
+use utils::{parse_num, parse_static, read_input};
+
+/// Base type for a crate
+#[derive(Debug, Clone)]
+struct Crate<'a> {
+    letter: char,
+    below: Cell<Option<&'a Crate<'a>>>,
+}
+
+impl Default for Crate<'_> {
+    fn default() -> Self {
+        Crate {
+            letter: ' ',
+            below: None.into(),
+        }
+    }
+}
+
+/// A move the crane may make
+#[derive(Debug, Clone, Copy)]
+struct Move {
+    reps: usize,
+    from: usize,
+    to: usize,
+}
+type Tops<'arena> = Vec<Option<&'arena Crate<'arena>>>;
+
+fn main() {
+    let input = read_input();
+
+    {
+        let arena = Bump::new();
+        let mut tops = construct_piles(&input, &arena);
+        for mv in parse_moves(&input) {
+            perform_move_9000(&mut tops, mv);
+        }
+
+        println!("Part 1: {}", top_letters(tops));
+    }
+
+    {
+        let arena = Bump::new();
+        let mut tops = construct_piles(&input, &arena);
+        for mv in parse_moves(&input) {
+            perform_move_9001(&mut tops, mv);
+        }
+
+        println!("Part 2: {}", top_letters(tops));
+    }
+}
+
+/// Get the message / the top letters of each stack
+fn top_letters(tops: Tops<'_>) -> String {
+    tops.iter().map(|x| x.as_ref().unwrap().letter).collect()
+}
+
+/// Perform a move for part 1
+fn perform_move_9000(tops: &mut Tops<'_>, mv: Move) {
+    for _ in 0..mv.reps {
+        let from = tops[mv.from].take().unwrap();
+        let to = tops[mv.to].take();
+
+        tops[mv.from] = from.below.replace(to);
+        tops[mv.to] = Some(from);
+    }
+}
+
+/// Perform a move for part 2
+fn perform_move_9001(tops: &mut Tops<'_>, mv: Move) {
+    let pickup_top = tops[mv.from].take().unwrap();
+
+    let mut pickup_bot = pickup_top;
+    for _ in 1..mv.reps {
+        pickup_bot = pickup_bot.below.get().as_ref().unwrap();
+    }
+
+    let to = tops[mv.to].take();
+
+    tops[mv.from] = pickup_bot.below.replace(to);
+    tops[mv.to] = Some(pickup_top);
+}
+
+// Annoying parsing code!
+
+fn construct_piles<'a>(input: &str, arena: &'a Bump) -> Tops<'a> {
+    let mut piles = Vec::new();
+    for layer_iter in input
+        .lines()
+        .take_while(|x| x.chars().find(|x| *x != ' ').unwrap() == '[')
+        .map(|x| x.chars().skip(1).step_by(4))
+    {
+        for (stack, chr) in layer_iter.enumerate() {
+            if piles.len() < stack + 1 {
+                piles.resize(stack + 1, None);
+            }
+
+            if chr != ' ' {
+                let val = &*arena.alloc(Crate {
+                    letter: chr,
+                    below: None.into(),
+                });
+                if piles[stack].is_none() {
+                    piles[stack] = Some(val);
+                } else {
+                    let mut top = *piles[stack].as_ref().unwrap();
+                    while let Some(below) = top.below.get() {
+                        top = below;
+                    }
+
+                    top.below.set(Some(val));
+                }
+            }
+        }
+    }
+
+    piles
+}
+
+fn parse_moves(input: &str) -> impl Iterator<Item = Move> + '_ {
+    input
+        .lines()
+        .skip_while(|line| !line.starts_with('m'))
+        .map(|line| {
+            let line = parse_static("move ", line);
+            let (reps, line) = parse_num(line);
+            let line = parse_static(" from ", line);
+            let (from, line) = parse_num::<usize>(line);
+            let line = parse_static(" to ", line);
+            let (to, _) = parse_num::<usize>(line);
+
+            Move {
+                reps,
+                from: from - 1,
+                to: to - 1,
+            }
+        })
+}