From 522e10a3eab301ccc2e6c1c56bff3cc757eb93d9 Mon Sep 17 00:00:00 2001
From: Keenan Tims <ktims@gotroot.ca>
Date: Mon, 8 Dec 2025 13:16:53 -0800
Subject: [PATCH] day8: add heap-based impl

---
 src/day8.rs | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 92 insertions(+), 3 deletions(-)

diff --git a/src/day8.rs b/src/day8.rs
index a0b31ea..f4ed5a6 100644
--- a/src/day8.rs
+++ b/src/day8.rs
@@ -1,4 +1,4 @@
-use std::fmt::Display;
+use std::{cmp::Reverse, collections::BinaryHeap, fmt::Display};
 
 use aoc_runner_derive::{aoc, aoc_generator};
 use itertools::Itertools;
@@ -112,12 +112,12 @@ fn part1_impl(input: &Circuits, n: usize) -> u64 {
         .unwrap() as u64
 }
 
-#[aoc(day8, part1)]
+#[aoc(day8, part1, Sorted)]
 fn part1(input: &Circuits) -> u64 {
     part1_impl(input, 1000)
 }
 
-#[aoc(day8, part2)]
+#[aoc(day8, part2, Sorted)]
 fn part2(input: &Circuits) -> u64 {
     let mut circuits = input.clone();
 
@@ -138,6 +138,85 @@ fn part2(input: &Circuits) -> u64 {
     panic!()
 }
 
+struct JunctionPair {
+    a: usize,
+    b: usize,
+    d: u64,
+}
+impl Eq for JunctionPair {}
+impl PartialEq for JunctionPair {
+    fn eq(&self, other: &Self) -> bool {
+        self.d == other.d
+    }
+}
+impl PartialOrd for JunctionPair {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.d.cmp(&other.d))
+    }
+}
+impl Ord for JunctionPair {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.d.cmp(&other.d)
+    }
+}
+
+fn make_heap(circuits: &Circuits) -> BinaryHeap<Reverse<JunctionPair>> {
+    BinaryHeap::from_iter(
+        circuits
+            .junctions
+            .iter()
+            .enumerate()
+            .tuple_combinations()
+            .map(|((a_pos, a), (b_pos, b))| {
+                Reverse(JunctionPair {
+                    a: a_pos,
+                    b: b_pos,
+                    d: a.squared_distance(b),
+                })
+            }),
+    )
+}
+
+fn part1_heaped_impl(input: &Circuits, n: usize) -> u64 {
+    let mut circuits = input.clone();
+    let mut distances = make_heap(&circuits);
+
+    for _ in 0..n {
+        let pair = distances.pop().unwrap().0;
+        circuits.connect(pair.a, pair.b);
+    }
+
+    circuits
+        .circuits
+        .iter()
+        .map(|c| c.len())
+        .sorted_unstable()
+        .rev()
+        .take(3)
+        .reduce(|a, b| a * b)
+        .unwrap() as u64
+}
+
+#[aoc(day8, part1, Heaped)]
+fn part1_heaped(input: &Circuits) -> u64 {
+    part1_heaped_impl(input, 1000)
+}
+
+#[aoc(day8, part2, Heaped)]
+fn part2_heaped(input: &Circuits) -> u64 {
+    let mut circuits = input.clone();
+    let mut distances = make_heap(&circuits);
+
+    while let Some(Reverse(jp)) = distances.pop() {
+        circuits.connect(jp.a, jp.b);
+        if circuits.circuits.len() == 1 {
+            return (circuits.junctions[jp.a].pos.0 * circuits.junctions[jp.b].pos.0) as u64;
+        }
+    }
+
+    panic!()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -168,8 +247,18 @@ mod tests {
         assert_eq!(part1_impl(&parse(EXAMPLE), 10), 40);
     }
 
+    #[test]
+    fn part1_heaped_example() {
+        assert_eq!(part1_heaped_impl(&parse(EXAMPLE), 10), 40);
+    }
+
     #[test]
     fn part2_example() {
         assert_eq!(part2(&parse(EXAMPLE)), 25272);
     }
+
+    #[test]
+    fn part2_heaped_example() {
+        assert_eq!(part2_heaped(&parse(EXAMPLE)), 25272);
+    }
 }