From 73765e857aad685ab8fc3bab451bc03395e94902 Mon Sep 17 00:00:00 2001
From: Keenan Tims <ktims@gotroot.ca>
Date: Fri, 5 Dec 2025 01:09:32 -0800
Subject: [PATCH] day5: bugfixes for rangeset

---
 src/day5.rs | 64 +++++++++++++++++++++++++++--------------------------
 1 file changed, 33 insertions(+), 31 deletions(-)

diff --git a/src/day5.rs b/src/day5.rs
index a2f6131..50958e0 100644
--- a/src/day5.rs
+++ b/src/day5.rs
@@ -1,4 +1,4 @@
-use std::cmp::{max, min};
+use std::cmp::max;
 use std::fmt::Debug;
 use std::ops::RangeInclusive;
 
@@ -43,45 +43,47 @@ impl RangeSet {
         Self { ranges: Vec::new() }
     }
     fn simplify(&mut self) {
-        // sort the ranges by start
         if self.ranges.len() < 2 {
             return;
         }
         let mut modified = true;
         while modified {
-            let mut new_ranges = Vec::new();
             modified = false;
+            // sort the ranges by start
             self.ranges.sort_by_key(|s| s.start);
-            for chunk in self.ranges.chunks(2) {
-                if chunk.len() == 1 {
-                    new_ranges.push(chunk[0].clone());
-                    continue;
+            let mut new_ranges = Vec::new();
+            let mut pos = 1;
+
+            while pos <= self.ranges.len() {
+                // part of a disgusting hack to avoid skipping or double adding at the end
+                if pos == self.ranges.len() {
+                    pos -= 1;
                 }
-                let (l, r) = (&chunk[0], &chunk[1]);
+                let (l, r) = (&self.ranges[pos - 1], &self.ranges[pos]);
+
                 if r.start <= l.end + 1 {
                     modified = true;
-                    new_ranges.push((min(r.start, l.start), max(l.end, r.end)).into())
-                } else {
-                    new_ranges.push(l.clone());
-                    new_ranges.push(r.clone());
-                }
-            }
-            if !self.ranges.len().is_multiple_of(2) && new_ranges.len() >= 2 {
-                let (l, r) = (new_ranges.pop().unwrap(), new_ranges.pop().unwrap());
-                if r.start <= l.end + 1 && r.end >= l.start - 1 {
-                    modified = true;
-                    new_ranges.push((min(r.start, l.start), max(l.end, r.end)).into())
+                    new_ranges.push((l.start, max(l.end, r.end)).into());
+                    // if we merged, skip checking the next range to avoid double-adding it
+                    // this screws us up at the very end, so need the disgusting hack above
+                    pos += 2;
+                } else if pos < self.ranges.len() - 1 {
+                    // keep only the lhs if we didn't merge
+                    new_ranges.push(l.clone());
+                    pos += 1;
                 } else {
+                    // at the end, keep both sides, otherwise the rhs gets excluded (if it didn't merge)
                     new_ranges.push(l.clone());
                     new_ranges.push(r.clone());
+                    pos += 2;
                 }
             }
+
             self.ranges = new_ranges;
         }
     }
     fn add(&mut self, s: Span) {
         self.ranges.push(s);
-        self.simplify()
     }
 }
 
@@ -111,6 +113,15 @@ fn parse(input: &str) -> Database {
     }
 }
 
+#[aoc(day5, part1)]
+fn part1(input: &Database) -> u64 {
+    input
+        .available_ingredients
+        .iter()
+        .filter(|i| input.fresh_ingredients.iter().any(|r| r.contains(i)))
+        .count() as u64
+}
+
 #[aoc_generator(day5, part2)]
 fn parse2(input: &str) -> Database2 {
     let mut fresh_ingredients = Vec::new();
@@ -124,22 +135,13 @@ fn parse2(input: &str) -> Database2 {
     Database2 { fresh_ingredients }
 }
 
-#[aoc(day5, part1)]
-fn part1(input: &Database) -> u64 {
-    input
-        .available_ingredients
-        .iter()
-        .filter(|i| input.fresh_ingredients.iter().any(|r| r.contains(i)))
-        .count() as u64
-}
-
 #[aoc(day5, part2)]
 fn part2(input: &Database2) -> u64 {
     let mut all_ingredients = RangeSet::new();
     for r in &input.fresh_ingredients {
-        all_ingredients.add(r.clone())
+        all_ingredients.add(r.clone());
     }
-
+    all_ingredients.simplify();
     all_ingredients.ranges.iter().map(|r| r.len()).sum::<u64>()
 }