From 6f3f655eb7f0390d8b75170226bf7b8d0178df2b Mon Sep 17 00:00:00 2001
From: traxys <quentin@familleboyer.net>
Date: Mon, 8 Dec 2025 14:53:04 +0100
Subject: [PATCH] Use a binary heap for day8

---
 src/bin/day8.rs | 51 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 45 insertions(+), 6 deletions(-)

diff --git a/src/bin/day8.rs b/src/bin/day8.rs
index ab31427..e8eea5e 100644
--- a/src/bin/day8.rs
+++ b/src/bin/day8.rs
@@ -1,4 +1,4 @@
-use std::time::Instant;
+use std::{collections::BinaryHeap, time::Instant};
 
 use aoc_2025::{load, print_res};
 use bstr::BString;
@@ -144,16 +144,55 @@ pub fn part1(input: Parsed) {
 
 #[inline(never)]
 pub fn part2(input: Parsed) {
-    let mut pairs: Vec<_> = (0..input.len())
-        .flat_map(|ia| ((ia + 1)..input.len()).map(move |ib| (ia, ib)))
+    struct PointPair<'a> {
+        a: &'a Point3,
+        b: &'a Point3,
+        ia: usize,
+        ib: usize,
+        dist2: u64,
+    }
+
+    impl<'a> Eq for PointPair<'a> {}
+
+    impl<'a> PartialEq for PointPair<'a> {
+        fn eq(&self, other: &Self) -> bool {
+            self.dist2.eq(&other.dist2)
+        }
+    }
+
+    impl<'a> PartialOrd for PointPair<'a> {
+        fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+            Some(self.cmp(other))
+        }
+    }
+
+    impl<'a> Ord for PointPair<'a> {
+        fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+            self.dist2.cmp(&other.dist2)
+        }
+    }
+
+    let pp = |ia, ib| {
+        let a = &input[ia];
+        let b = &input[ib];
+        PointPair {
+            a,
+            ia,
+            b,
+            ib,
+            dist2: a.dist2(b),
+        }
+    };
+
+    let pairs: BinaryHeap<_> = (0..input.len())
+        .flat_map(|ia| ((ia + 1)..input.len()).map(move |ib| pp(ia, ib)))
         .collect();
-    pairs.sort_unstable_by_key(|&(ia, ib)| input[ia].dist2(&input[ib]));
 
     let mut uf = UnionFind::new(input.len());
-    for &(ia, ib) in &pairs {
+    for &PointPair { ia, ib, a, b, .. } in pairs.iter() {
         uf.union(ia as u16, ib as u16);
         if uf.set_count() == 1 {
-            print_res!("X product of last boxes: {}", input[ia].x * input[ib].x);
+            print_res!("X product of last boxes: {}", a.x * b.x);
             return;
         }
     }