added code to generate landmarks with the greedy algorithm

src/bin/gen_landmarks_greedy.rs

@@ -0,0 +1,93 @@
+use bincode;
+use clap::Parser;
+use fapra_osm_2::alt::{LandmarkSet, Landmark};
+use fapra_osm_2::gridgraph::{GridGraph, EdgeCost};
+use std::fs::File;
+use std::io::prelude::*;
+use std::process::exit;
+
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about=None)]
+struct Args {
+    /// the FMI file to load
+    #[clap(short, long)]
+    input: String,
+
+    /// the file to which to write the landmarks
+    #[clap(short, long)]
+    output: String,
+
+    /// the amount of landmarks to generate
+    #[clap(short, long)]
+    amount: usize,
+}
+
+fn main() {
+    let args = Args::parse();
+
+    let file = match File::open(args.input.clone()) {
+        Ok(f) => f,
+        Err(e) => {
+            println!("Error while opening file: {}", e);
+            exit(1);
+        }
+    };
+
+    let graph = GridGraph::from_fmi_file(file).unwrap();
+    println!("finished loading graph from file");
+
+    let mut output = match File::create(args.output.clone()) {
+        Ok(f) => f,
+        Err(e) => {
+            println!("Error while creating the file {}: {}", args.output, e);
+            exit(2)
+        }
+    };
+
+    fn compute_next_index(costs: &mut Vec<EdgeCost>, landmark: &Landmark) -> usize {
+
+        let mut max_index = 0;
+        let mut max_cost = 0;
+
+        for (i, cost) in landmark.distances.iter().enumerate() {
+            if *cost < costs[i] {
+                costs[i] = *cost;
+            }
+
+            if costs[i] > max_cost && costs[i] != EdgeCost::MAX {
+                max_cost = costs[i];
+                max_index = i;
+            }
+        }
+
+        max_index
+    }
+
+    let initial_node = graph.get_random_node().unwrap();
+
+    println!("selected initial node: {:?}", initial_node);
+
+
+    let mut landmark = Landmark::generate(*initial_node, &graph);
+
+    let mut costs: Vec<EdgeCost> = landmark.distances.clone();
+
+    let mut set = LandmarkSet::default();
+
+    let mut next = compute_next_index(&mut costs, &landmark);
+    set.landmarks.push(landmark);
+
+    while set.landmarks.len() < args.amount {
+        let node = graph.nodes[next];
+
+        println!("the next node will be {:?} with a distance of {}", node, costs[node.index as usize]);
+
+        landmark = Landmark::generate(node, &graph);
+        next = compute_next_index(&mut costs, &landmark);
+        set.landmarks.push(landmark);
+    }
+
+    let encoded = bincode::serialize(&set).unwrap();
+
+    output.write_all(&encoded).expect("Error while writing LandmarkSet data");
+}