[rs] Solve 2022_13 part 1

rs/src/y2022/d13.rs

@@ -0,0 +1,100 @@
+use std::cmp::Ordering;
+use std::fmt;
+use std::iter::Peekable;
+use std::str::Chars;
+
+enum Message {
+    Int(u32),
+    List(Vec<Message>),
+}
+
+impl fmt::Debug for Message {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Int(int) => int.fmt(f),
+            Self::List(list) => f.debug_list().entries(list).finish(),
+        }
+    }
+}
+
+impl Ord for Message {
+    fn cmp(&self, other: &Self) -> Ordering {
+        match (self, other) {
+            (Self::Int(x), Self::Int(y)) => x.cmp(y),
+            (Self::Int(x), Self::List(ys)) => vec![Self::Int(*x)].cmp(ys),
+            (Self::List(xs), Self::Int(y)) => xs.cmp(&vec![Self::Int(*y)]),
+            (Self::List(xs), Self::List(ys)) => xs.cmp(ys),
+        }
+    }
+}
+
+impl PartialOrd for Message {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Eq for Message {}
+
+impl PartialEq for Message {
+    fn eq(&self, other: &Self) -> bool {
+        self.cmp(other) == Ordering::Equal
+    }
+}
+
+type CharIter<'a> = Peekable<Chars<'a>>;
+
+fn parse_int(chars: &mut CharIter) -> u32 {
+    let mut result = 0;
+    while let Some(char) = chars.peek() {
+        if !char.is_ascii_digit() {
+            break;
+        }
+        result = result * 10 + (*char as u32 - '0' as u32);
+        chars.next();
+    }
+    result
+}
+
+fn parse_list(chars: &mut CharIter) -> Vec<Message> {
+    let mut result = vec![];
+    assert_eq!(chars.next(), Some('['));
+    if !matches!(chars.peek(), Some(']')) {
+        result.push(parse_message(chars));
+        while matches!(chars.peek(), Some(',')) {
+            chars.next();
+            result.push(parse_message(chars));
+        }
+    }
+    assert_eq!(chars.next(), Some(']'));
+    result
+}
+
+fn parse_message(chars: &mut CharIter) -> Message {
+    if matches!(chars.peek(), Some('[')) {
+        Message::List(parse_list(chars))
+    } else {
+        Message::Int(parse_int(chars))
+    }
+}
+
+pub fn solve(input: String) {
+    let pairs = input
+        .trim()
+        .split("\n\n")
+        .map(|p| {
+            let (fst, snd) = p.split_once('\n').unwrap();
+            let fst = parse_list(&mut fst.chars().peekable());
+            let snd = parse_list(&mut snd.chars().peekable());
+            (fst, snd)
+        })
+        .collect::<Vec<_>>();
+
+    let part1 = pairs
+        .iter()
+        .enumerate()
+        .filter(|(_, (fst, snd))| fst < snd)
+        .map(|(i, _)| i + 1)
+        .sum::<usize>();
+    println!("Part 1: {part1}");
+}