cleaned up the code

src/utils.rs

@@ -1,18 +1,23 @@
 use crate::alt::LandmarkSet;
-use crate::gridgraph::GridGraph;
+use crate::gridgraph::{EdgeCost, GridGraph};
 use serde::{Deserialize, Serialize};
+use std::cmp::Ordering;
 use std::fs::File;
 use std::io::BufReader;
 use std::process::exit;
 
+/// an approximation of the earths radius.
 pub const EARTH_RADIUS: f64 = 6_371_000.0; // meters
 
+/// serialization format for routing queries.
 #[derive(Serialize, Deserialize, Debug, Copy, Clone)]
 pub struct RoutingQuery {
     pub source: usize,
     pub destination: usize,
 }
 
+/// loads the graph from the given path.
+/// exits if an error occurs during loading.
 pub fn load_graph(path: &str) -> Box<GridGraph> {
     println!("Loading file from {}", path);
     let file = match File::open(path) {
@@ -36,6 +41,8 @@ pub fn load_graph(path: &str) -> Box<GridGraph> {
     graph
 }
 
+/// loads a set of landmarks from the given path.
+/// exits if an error occurs during loading.
 pub fn load_landmarks(path: &str) -> LandmarkSet {
     let landmarks = match File::open(path) {
         Ok(f) => f,
@@ -47,3 +54,25 @@ pub fn load_landmarks(path: &str) -> LandmarkSet {
 
     bincode::deserialize_from(BufReader::new(landmarks)).unwrap()
 }
+
+/// A heap element for Dijkstra's algorithm.
+///
+/// The comparison functions are inverted, so that Rusts MaxHeap works as a
+/// MinHeap.
+#[derive(Eq, PartialEq)]
+pub struct DijkstraElement {
+    pub index: u32,
+    pub cost: EdgeCost,
+}
+
+impl Ord for DijkstraElement {
+    fn cmp(&self, other: &Self) -> Ordering {
+        other.cost.cmp(&self.cost)
+    }
+}
+
+impl PartialOrd for DijkstraElement {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}