From 4a407de45bc4afd9682b7d22e789f9eea79ae018 Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Wed, 15 Dec 2021 13:56:18 -0500
Subject: [PATCH] Use BinaryHeap for day15 dijkstra

---
 Cargo.toml   |  3 +++
 src/day15.rs | 37 +++++++++++++++++--------------------
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 471ab37..49c8df8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,3 +8,6 @@ edition = "2021"
 [dependencies]
 itertools = "0.10.3"
 ansi_term = "0.12.1"
+
+[profile.release]
+debug = true
diff --git a/src/day15.rs b/src/day15.rs
index 3c4e814..508fdab 100644
--- a/src/day15.rs
+++ b/src/day15.rs
@@ -1,4 +1,4 @@
-use std::collections::{HashMap, HashSet};
+use std::collections::BinaryHeap;
 
 pub fn day15() {
     // let input = r#"
@@ -21,7 +21,7 @@ pub fn day15() {
     let graph: Graph<100> = input.into();
 
     let path = dijkstra(&graph, graph.size(), &(0, 0), &graph.bottom_right());
-    println!("found path: {:?}", path);
+    // println!("found path: {:?}", path);
     println!("path risk: {}", path_risk(&graph, &path.unwrap()));
 
     let path = dijkstra(
@@ -30,7 +30,7 @@ pub fn day15() {
         &(0, 0),
         &(graph.size() * 5 - 1, graph.size() * 5 - 1),
     );
-    println!("{:?}", path);
+    // println!("{:?}", path);
     println!("path risk: {}", path_risk(&graph, &path.unwrap()));
 }
 
@@ -88,21 +88,15 @@ fn dijkstra<const N: usize>(
     source: &Point,
     target: &Point,
 ) -> Option<Vec<Point>> {
-    let mut q: HashSet<Point> = HashSet::new();
-    let mut dist = vec![vec![0; size]; size];
+    let mut q: BinaryHeap<(isize, Point)> = BinaryHeap::new();
+    let mut dist = vec![vec![usize::MAX; size]; size];
     let mut prev = vec![vec![None; size]; size];
 
-    for x in 0..size {
-        for y in 0..size {
-            dist[x][y] = usize::max_value();
-            q.insert((x, y));
-        }
-    }
     dist[source.0][source.1] = 0;
+    q.push((0, *source));
 
-    while let Some(u) = q.iter().min_by_key(|p| dist[p.0][p.1]) {
-        let u = u.clone();
-        q.remove(&u);
+    while let Some((neg_cost, u)) = q.pop() {
+        let cost = -neg_cost as usize;
 
         if u == *target {
             let mut s = vec![];
@@ -114,13 +108,16 @@ fn dijkstra<const N: usize>(
             return Some(s);
         }
 
+        if cost > dist[u.0][u.1] {
+            continue;
+        }
+
         for v in neighbors(u, size) {
-            if q.contains(&v) {
-                let alt = dist[u.0][u.1] + g.risk(&v);
-                if alt < dist[v.0][v.1] {
-                    dist[v.0][v.1] = alt;
-                    prev[v.0][v.1] = Some(u);
-                }
+            let alt = dist[u.0][u.1] + g.risk(&v);
+            if alt < dist[v.0][v.1] {
+                dist[v.0][v.1] = alt;
+                prev[v.0][v.1] = Some(u);
+                q.push((-(alt as isize), v));
             }
         }
     }