From 8d117c794835091d3c3416fc5944149372bd369c Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Thu, 23 Dec 2021 12:18:46 -0500
Subject: factor out pathfinding

---
 src/graph.rs | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 src/graph.rs

(limited to 'src/graph.rs')

diff --git a/src/graph.rs b/src/graph.rs
new file mode 100644
index 0000000..831cc17
--- /dev/null
+++ b/src/graph.rs
@@ -0,0 +1,54 @@
+use crate::prelude::*;
+
+pub trait Graph<Vertex, Edge>
+where
+    Vertex: std::hash::Hash + Clone + Copy + PartialEq + Eq + std::fmt::Debug,
+{
+    type Edges: IntoIterator<Item = Edge>;
+
+    fn edges(&self, v: Vertex) -> Self::Edges;
+    fn edge(&self, v: Vertex, e: Edge) -> (Vertex, i64);
+
+    fn dijkstra(&self, start: Vertex, end: Vertex) -> (i64, Vec<Vertex>) {
+        let mut to_visit = priority_queue::PriorityQueue::new();
+        let mut prev = HashMap::new();
+        prev.insert(start, start);
+        to_visit.push(start, std::cmp::Reverse(0));
+        while let Some((v, std::cmp::Reverse(distance))) = to_visit.pop() {
+            if v == end {
+                let mut path = vec![v];
+                let mut cur = v;
+                while let Some(next) = prev.get(&cur) {
+                    if *next == cur {
+                        break;
+                    }
+                    path.insert(0, *next);
+                    cur = *next;
+                }
+                return (distance, path);
+            }
+
+            for e in self.edges(v) {
+                let (next, weight) = self.edge(v, e);
+                let visited = prev.contains_key(&next);
+                let new_distance = distance + weight;
+                if to_visit.get(&next).is_some() {
+                    prev.insert(next, v);
+                    if new_distance < to_visit.get_priority(&next).unwrap().0
+                    {
+                        to_visit.change_priority(
+                            &next,
+                            std::cmp::Reverse(new_distance),
+                        );
+                    }
+                } else {
+                    if !visited {
+                        prev.insert(next, v);
+                        to_visit.push(next, std::cmp::Reverse(new_distance));
+                    }
+                }
+            }
+        }
+        unreachable!()
+    }
+}
-- 
cgit v1.2.3-54-g00ecf