1 files changed, 153 insertions, 0 deletions
diff --git a/2022/Rust/src/day13.rs b/2022/Rust/src/day13.rs
new file mode 100644
index 0000000..b07e515
--- /dev/null
+++ b/2022/Rust/src/day13.rs
@@ -0,0 +1,153 @@
+use std::{cmp::Ordering, fmt, str::FromStr};
+
+#[derive(PartialEq, Eq, Clone)]
+enum ListItem {
+    List(Vec<ListItem>),
+    Number(usize),
+}
+
+impl fmt::Debug for ListItem {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ListItem::List(arr) => f.debug_list().entries(arr.iter()).finish(),
+            ListItem::Number(num) => write!(f, "{}", num),
+        }
+    }
+}
+
+impl ListItem {
+    fn with_slice<T>(&self, f: impl FnOnce(&[ListItem]) -> T) -> T {
+        match self {
+            Self::List(n) => f(&n[..]),
+            Self::Number(n) => f(&[Self::Number(*n)]),
+        }
+    }
+}
+
+impl std::cmp::Ord for ListItem {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.partial_cmp(other).unwrap()
+    }
+}
+
+impl PartialOrd for ListItem {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        match (self, other) {
+            (ListItem::Number(a), ListItem::Number(b)) => a.partial_cmp(b),
+            (l, r) => l.with_slice(|l| r.with_slice(|r| l.partial_cmp(r))),
+        }
+    }
+}
+
+impl FromStr for ListItem {
+    type Err = String;
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        // Remove whitespace from input
+        let input = input.trim();
+
+        // Check if input is empty
+        if input.is_empty() {
+            return Ok(ListItem::List(vec![]));
+        }
+
+        // Check if input is a number
+        if let Ok(num) = input.parse::<usize>() {
+            return Ok(ListItem::Number(num));
+        }
+
+        // Check if input is a list
+        if input.starts_with('[') && input.ends_with(']') {
+            // Remove brackets from input
+            let input = &input[1..input.len() - 1];
+
+            // Split input by commas
+            let mut items = Vec::new();
+            let mut start = 0;
+            let mut level = 0;
+            for (i, c) in input.char_indices() {
+                match c {
+                    '[' => level += 1,
+                    ']' => level -= 1,
+                    ',' if level == 0 => {
+                        // Parse a list item
+                        let item = ListItem::from_str(&input[start..i])?;
+                        items.push(item);
+                        start = i + 1;
+                    }
+                    _ => {}
+                }
+            }
+            // Parse the last list item
+            let item = ListItem::from_str(&input[start..])?;
+            items.push(item);
+
+            return Ok(ListItem::List(items));
+        }
+
+        // Invalid input
+        Err("Invalid input".to_string())
+    }
+}
+
+type Packet = ListItem;
+
+#[derive(Debug)]
+struct PacketPair {
+    left: Packet,
+    right: Packet,
+}
+
+// [[1],[2,3,4]]
+fn solve_part_one(data: &str) -> usize {
+    let packets_pairs: Vec<&str> = data.split("\n\n").collect();
+    let mut packets: Vec<PacketPair> = vec![];
+    for pair in packets_pairs {
+        let (first, last) = pair
+            .split_once("\n")
+            .expect("Should be splittable by newline");
+        let first = ListItem::from_str(first).unwrap();
+        let last = ListItem::from_str(last).unwrap();
+        packets.push(PacketPair {
+            left: first,
+            right: last,
+        });
+    }
+    let mut ans = 0;
+    for (i, pair) in packets.iter().enumerate() {
+        if pair.left < pair.right {
+            ans += i + 1;
+        }
+    }
+    ans
+}
+
+fn solve_part_two(data: &str) -> usize {
+    let dividers = vec![
+        Packet::List(vec![Packet::Number(2)]),
+        Packet::List(vec![Packet::Number(6)]),
+    ];
+
+    let mut packets = data
+        .lines()
+        .filter(|s| !s.is_empty())
+        .map(|line| Packet::from_str(line).unwrap())
+        .chain(dividers.iter().cloned())
+        .collect::<Vec<_>>();
+
+    packets.sort();
+
+    dividers
+        .iter()
+        .map(|d| packets.binary_search(d).unwrap() + 1)
+        .product::<usize>()
+}
+
+fn main() {
+    let test = include_str!("../input/day13.test");
+    let prod = include_str!("../input/day13.prod");
+    println!("Part1_test : {}", solve_part_one(test));
+    println!("Part1_prod : {}", solve_part_one(prod));
+    println!("{}", solve_part_two(test));
+    println!("{}", solve_part_two(prod));
+}