Day 13

diff --git a/src/day13.rs b/src/day13.rs
new file mode 100644 (file)
index 0000000..4018d53
--- /dev/null
+++ b/src/day13.rs
@@ -0,0 +1,186 @@
+use std::cmp::{Ord, Ordering, PartialOrd};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Signal {
+    Value(i32),
+    List(Vec<Signal>),
+}
+
+impl Signal {
+    fn parse(s: &str) -> Self {
+        fn parse_chars<'a>(chars: &mut impl Iterator<Item = &'a [char]>) -> Signal {
+            let mut n = String::new();
+            let mut l: Vec<Signal> = Vec::new();
+            while let Some([c1, c2]) = chars.next() {
+                match c1 {
+                    '[' => {
+                        if *c2 == ']' {
+                            chars.next();
+                            return Signal::List(l);
+                        }
+                        l.push(parse_chars(chars));
+                    }
+                    ']' => return Signal::List(l),
+                    ',' => l.push(parse_chars(chars)),
+                    _ if c1.is_digit(10) => {
+                        n.push(*c1);
+                        if !c2.is_digit(10) {
+                            return Signal::Value(n.parse().unwrap());
+                        }
+                    }
+                    _ => (),
+                }
+            }
+            Signal::Value(n.parse().unwrap())
+        }
+        let mut chars = s.replace(" ", "").chars().collect::<Vec<char>>();
+        // Add a space because only the first character of 'windows(2)' is processed.
+        chars.push(' ');
+        parse_chars(&mut chars.windows(2))
+    }
+}
+
+impl PartialOrd for Signal {
+    fn partial_cmp(&self, other: &Signal) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Signal {
+    fn cmp(&self, other: &Signal) -> Ordering {
+        match (self, other) {
+            (Signal::Value(v1), Signal::Value(v2)) => v1.cmp(v2),
+            (v1 @ Signal::Value(_), l2 @ Signal::List(_)) => Signal::List(vec![v1.clone()]).cmp(l2),
+            (l1 @ Signal::List(_), v2 @ Signal::Value(_)) => {
+                l1.cmp(&Signal::List(vec![v2.clone()]))
+            }
+            (Signal::List(l1), Signal::List(l2)) => {
+                for i in 0..l1.len().min(l2.len()) {
+                    match l1[i].cmp(&l2[i]) {
+                        Ordering::Equal => (),
+                        other => return other,
+                    }
+                }
+                l1.len().cmp(&l2.len())
+            }
+        }
+    }
+}
+
+pub fn parse(input: &str) -> Vec<Signal> {
+    input
+        .lines()
+        .filter(|l| !l.is_empty())
+        .map(Signal::parse)
+        .collect()
+}
+
+pub fn sum_indices_signals_in_the_right_order(signals: &[Signal]) -> usize {
+    signals.chunks(2).enumerate().fold(0, |sum, (n, chunk)| {
+        if chunk[0] < chunk[1] {
+            sum + n + 1
+        } else {
+            sum
+        }
+    })
+}
+
+pub fn product_indices_special_signals(signals: &[Signal]) -> usize {
+    let mut signals = Vec::from(signals);
+    let s1 = Signal::parse("[[2]]");
+    let s2 = Signal::parse("[[6]]");
+    signals.push(s1.clone());
+    signals.push(s2.clone());
+    signals.sort();
+    (signals.binary_search(&s1).unwrap() + 1) * (signals.binary_search(&s2).unwrap() + 1)
+}
+
+// pub fn sort(signals: &vec[])
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_tests() {
+        assert_eq!(Signal::parse("[]"), Signal::List(Vec::new()));
+        assert_eq!(Signal::parse("1"), Signal::Value(1));
+        assert_eq!(Signal::parse("123"), Signal::Value(123));
+        assert_eq!(Signal::parse("[1]"), Signal::List(vec![Signal::Value(1)]));
+        assert_eq!(
+            Signal::parse("[1,[]]"),
+            Signal::List(vec![Signal::Value(1), Signal::List(Vec::new())])
+        );
+        assert_eq!(
+            Signal::parse("[[], 1]"),
+            Signal::List(vec![Signal::List(Vec::new()), Signal::Value(1)])
+        );
+        assert_eq!(
+            Signal::parse(" [   1,[  [ ] ,2  ]   ]  "),
+            Signal::List(vec![
+                Signal::Value(1),
+                Signal::List(vec![Signal::List(Vec::new()), Signal::Value(2)])
+            ])
+        );
+    }
+
+    #[test]
+    fn comparison() {
+        assert!(Signal::parse("[1,1,3,1,1]")
+            .cmp(&Signal::parse("[1,1,5,1,1]"))
+            .is_lt());
+        assert!(Signal::parse("[[1],[2,3,4]]")
+            .cmp(&Signal::parse("[[1],4]"))
+            .is_lt());
+        assert!(Signal::parse("[9]")
+            .cmp(&Signal::parse("[[8,7,6]]"))
+            .is_gt());
+        assert!(Signal::parse("[[4,4],4,4]")
+            .cmp(&Signal::parse("[[4,4],4,4,4]"))
+            .is_lt());
+        assert!(Signal::parse("[7,7,7,7]")
+            .cmp(&Signal::parse("[7,7,7]"))
+            .is_gt());
+        assert!(Signal::parse("[]").cmp(&Signal::parse("[3]")).is_lt());
+        assert!(Signal::parse("[[[]]]").cmp(&Signal::parse("[[]]")).is_gt());
+        assert!(Signal::parse("[1,[2,[3,[4,[5,6,7]]]],8,9]")
+            .cmp(&Signal::parse("[1,[2,[3,[4,[5,6,0]]]],8,9]"))
+            .is_gt());
+    }
+
+    static SIGNALS: &str = "[1,1,3,1,1]
+        [1,1,5,1,1]
+
+        [[1],[2,3,4]]
+        [[1],4]
+
+        [9]
+        [[8,7,6]]
+
+        [[4,4],4,4]
+        [[4,4],4,4,4]
+
+        [7,7,7,7]
+        [7,7,7]
+
+        []
+        [3]
+
+        [[[]]]
+        [[]]
+
+        [1,[2,[3,[4,[5,6,7]]]],8,9]
+        [1,[2,[3,[4,[5,6,0]]]],8,9]";
+
+    #[test]
+    fn part1() {
+        let signals = parse(SIGNALS);
+        assert_eq!(sum_indices_signals_in_the_right_order(&signals), 13);
+    }
+
+    #[test]
+    fn part2() {
+        let signals = parse(SIGNALS);
+        assert_eq!(product_indices_special_signals(&signals), 140);
+    }
+}