2024 day 5

Author: ictrobot

crates/year2024/examples/day05_example0.txt

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47

crates/year2024/src/day05.rs

@@ -0,0 +1,96 @@
+use utils::prelude::*;
+
+/// Sorting lists using a partial order of constraints.
+#[derive(Clone, Debug)]
+pub struct Day05 {
+    rules: Rules,
+    sorted: Vec<Vec<u32>>,
+    unsorted: Vec<Vec<u32>>,
+}
+
+const MIN_NUM: usize = 10;
+const MAX_NUM: usize = 99;
+const RANGE: usize = MAX_NUM - MIN_NUM + 1;
+type Rules = [bool; RANGE * RANGE];
+
+impl Day05 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let num = parser::number_range(MIN_NUM as u32..=MAX_NUM as u32);
+        let rules_parser = num.then(num.with_prefix(b'|')).repeat(b'\n', 1);
+        let updates_parser = num.repeat(b',', 1).repeat(b'\n', 1);
+
+        let (rules_list, updates) = rules_parser
+            .then(updates_parser.with_prefix(b'\n'))
+            .parse_complete(input)?;
+
+        let mut rules = [false; RANGE * RANGE];
+        for (a, b) in rules_list {
+            rules[(a as usize - MIN_NUM) * RANGE + b as usize] = true;
+        }
+
+        let (sorted, unsorted) = updates.into_iter().partition(|update| {
+            for (i, &page1) in update.iter().enumerate() {
+                for &page2 in update.iter().skip(i + 1) {
+                    if Self::must_be_before(&rules, page2, page1) {
+                        return false;
+                    }
+                }
+            }
+            true
+        });
+
+        Ok(Self {
+            rules,
+            sorted,
+            unsorted,
+        })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u32 {
+        self.sorted
+            .iter()
+            .map(|update| update[update.len() / 2])
+            .sum()
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> u32 {
+        let mut result = 0;
+        let mut list = Vec::new();
+        for original in &self.unsorted {
+            original.clone_into(&mut list);
+
+            for _ in 0..(list.len() / 2) {
+                let i = Self::find_first_index(&self.rules, &list);
+                list.swap_remove(i);
+            }
+
+            let i = Self::find_first_index(&self.rules, &list);
+            result += list[i];
+        }
+
+        result
+    }
+
+    fn must_be_before(rules: &Rules, page1: u32, page2: u32) -> bool {
+        rules[(page1 as usize - MIN_NUM) * RANGE + page2 as usize]
+    }
+
+    fn find_first_index(rules: &Rules, list: &[u32]) -> usize {
+        'outer: for (i, &page1) in list.iter().enumerate() {
+            for (j, &page2) in list.iter().enumerate() {
+                if i != j && Self::must_be_before(rules, page2, page1) {
+                    continue 'outer;
+                }
+            }
+
+            return i;
+        }
+        panic!("no solution found");
+    }
+}
+
+examples!(Day05 -> (u32, u32) [
+    {file: "day05_example0.txt", part1: 143, part2: 123},
+]);

crates/year2024/src/lib.rs

@@ -6,4 +6,5 @@ utils::year!(2024 => year2024, ${
     2 => day02::Day02,
     3 => day03::Day03,
     4 => day04::Day04,
+    5 => day05::Day05,
 });