1 files changed, 64 insertions, 0 deletions
diff --git a/src/bin/5.rs b/src/bin/5.rs
new file mode 100644
index 0000000..7295392
--- /dev/null
+++ b/src/bin/5.rs
@@ -0,0 +1,64 @@
+//! Awful...
+
+use std::{cmp::Ordering, collections::{HashMap, HashSet}, error::Error, fs::File, io::{BufRead, BufReader}};
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let f = File::open("input/5.test")?;
+    let mut f = BufReader::new(f);
+
+    let mut must_precede: HashMap<i64, HashSet<i64>> = HashMap::new();
+    let mut line = String::new();
+
+    loop {
+        line.clear();
+        f.read_line(&mut line)?;
+        let line = line.trim_end();
+        if line.is_empty() { break };
+        let (lhs, rhs) = line.split_once('|').ok_or("Invalid dependency line")?;
+        must_precede.entry(lhs.parse()?).or_default().insert(rhs.parse()?);
+    }
+
+    let mut pages: Vec<i64> = Vec::new();
+    let mut p1_total = 0;
+    let mut p2_total = 0;
+
+    loop {
+        line.clear();
+        if f.read_line(&mut line)? == 0 {
+            break;
+        };
+        pages.clear();
+        // Ugh...
+        pages.extend(line.trim_end().split(',').map(|p| p.parse::<i64>().unwrap()));
+        let mut valid = true;
+        'outer: for (i, page) in pages.iter().enumerate().skip(1) {
+            let Some(succ) = must_precede.get(page) else {
+                continue;
+            };
+            for p in &pages[0..i] {
+                if succ.contains(p) {
+                    valid = false;
+                    break 'outer;
+                }
+            }
+        }
+        if valid {
+            p1_total += pages[pages.len() / 2];
+        } else {
+            pages.sort_by(|a, b| {
+                if let Some(succ) = must_precede.get(a) {
+                    if succ.contains(b) {
+                        Ordering::Less
+                    } else {
+                        Ordering::Greater
+                    }
+                } else {
+                    Ordering::Equal
+                }
+            });
+            p2_total += pages[pages.len() / 2];
+        }
+    }
+    println!("{p1_total}\n{p2_total}");
+    Ok(())
+}