day 5 puzzle 2

progress.yaml

@@ -7,4 +7,4 @@
 4:
   stars: 2
 5:
-  stars: 1
+  stars: 2

src/day5/puzzle2.typ

@@ -0,0 +1,63 @@
+#import "/src/utils.typ": *
+
+#let make-rules-dict(rules) = {
+  let dict = (:)
+
+  for rule in rules {
+    let (a, b) = rule
+
+    if a not in dict {
+      dict.insert(a, ())
+    }
+    dict.at(a).push(b)
+  }
+
+  return dict
+}
+
+/// Bubble sort
+#let fix-update(dict, update) = {
+  let update = update
+
+  let has-changed = false
+  let changed = true
+  while changed {
+    changed = false
+    for i in range(update.len() - 1) {
+      let a = str(update.at(i))
+      let b = str(update.at(i + 1))
+      
+      if a in dict.at(b, default: ()) {
+        update.at(i) = int(b)
+        update.at(i + 1) = int(a)
+        changed = true
+        has-changed = true
+      }
+    }
+  }
+  return (has-changed, update)
+}
+
+#let solve(input) = {
+  let (rules, updates) = input.split("\n\n")
+  rules = rules.split("\n").map(l => l.split("|"))
+  updates = updates.split("\n").map(l => l.split(",").map(int))
+
+  let total = 0
+  let rules-dict = make-rules-dict(rules)
+
+  for update in updates {
+    let (has-changed, update) = fix-update(rules-dict, update)
+    if has-changed {
+      total += update.at(calc.div-euclid(update.len(), 2))
+    }
+  }
+
+  return total
+}
+
+#show-puzzle(
+  5, 2,
+  solve,
+  example: 123
+)