day5 solution 1

1 files changed, 100 insertions, 0 deletions

diff --git a/src/bin/day5.rs b/src/bin/day5.rs
new file mode 100644
index 0000000..d13be85
--- /dev/null
+++ b/src/bin/day5.rs
@@ -0,0 +1,100 @@
+use std::collections::{HashMap, HashSet};
+
+static DAY: u8 = 5;
+
+fn main() {
+    let input = advent::read_file(DAY);
+    println!("{DAY}a: {}", PageOrdering::new(&input).right_order_middle());
+    println!("{DAY}b: {}", 0);
+}
+
+struct PageOrdering {
+    rules: HashMap<u32,HashSet<u32>>,
+    updates: Vec<Vec<u32>>,
+}
+
+impl PageOrdering {
+    fn new(input: &str) -> PageOrdering {
+        let (rules_lines, updates_lines) = input.split_once("\n\n").unwrap();
+
+        let mut rules = HashMap::new();
+        for rule in rules_lines.split("\n") {
+            let (left, right) = rule.split_once("|").unwrap();
+            let left = left.parse::<u32>().unwrap();
+            let right = right.parse::<u32>().unwrap();
+            rules.entry(left).or_insert(HashSet::new()).insert(right);
+        }
+
+        let mut updates = Vec::new();
+        for line in updates_lines.split_terminator("\n") {
+            let update = line.split(",").map(|x| x.parse::<u32>().unwrap()).collect::<Vec<_>>();
+            updates.push(update);
+        }
+
+        PageOrdering { rules, updates }
+    }
+
+    fn correct_order(&self, update: &[u32]) -> bool {
+        for (i, page1) in update.iter().enumerate() {
+            for page2 in update.iter().skip(i+1) {
+                let before2 = match self.rules.get(page2) {
+                    Some(r) => r,
+                    None => continue,
+                };
+                if before2.contains(page1) {
+                    return false;
+                }
+            }
+        }
+        true
+    }
+
+    fn right_order_middle(&self) -> u32 {
+        let mut sum = 0;
+        for update in &self.updates {
+            if self.correct_order(update) {
+                sum += update[update.len()/2];
+            }
+        }
+        sum
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input =
+"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";
+        assert_eq!(PageOrdering::new(input).right_order_middle(), 143);
+    }
+}