From 53756b586c3e42186ca1c7744cf3231a99f815d7 Mon Sep 17 00:00:00 2001
From: Manuel Thalmann <m@nuth.ch>
Date: Tue, 1 Nov 2022 21:01:15 +0100
Subject: [PATCH] Implement Dijkstras algorithm

---
 .../java/ch/nuth/zhaw/exbox/RouteServer.java  | 70 ++++++++++++++++---
 1 file changed, 60 insertions(+), 10 deletions(-)

diff --git a/app/src/main/java/ch/nuth/zhaw/exbox/RouteServer.java b/app/src/main/java/ch/nuth/zhaw/exbox/RouteServer.java
index 13e541c..2e9db70 100644
--- a/app/src/main/java/ch/nuth/zhaw/exbox/RouteServer.java
+++ b/app/src/main/java/ch/nuth/zhaw/exbox/RouteServer.java
@@ -2,27 +2,75 @@ package ch.nuth.zhaw.exbox;
 
 import java.util.LinkedList;
 import java.util.List;
+import java.util.PriorityQueue;
+import java.util.Queue;
 
 public class RouteServer implements CommandExecutor {
     /**
-    build the graph given a text file with the topology
-    */
+     * build the graph given a text file with the topology
+     */
     public Graph<DijkstraNode, Edge> createGraph(String topo) throws Exception {
         // TODO implement
+        Graph<DijkstraNode, Edge> graph = new AdjListGraph<>(DijkstraNode.class, Edge.class);
+
+        for (String line : topo.split("\r?\n")) {
+            String[] attributes = line.split(" ");
+
+            try {
+                for (int i = 0; i <= 1; i++) {
+                    graph.addEdge(attributes[i], attributes[1 - i], Double.parseDouble(attributes[2]));
+                }
+            } catch (Throwable e) {
+                throw new Exception(e);
+            }
+        }
+
+        return graph;
     }
 
-
     /**
-    apply the dijkstra algorithm
-    */
+     * apply the dijkstra algorithm
+     */
     public void dijkstraRoute(Graph<DijkstraNode, Edge> graph, String from, String to) {
-        // TODO implement
+        Queue<DijkstraNode> pendingNodes = new PriorityQueue<>();
+        DijkstraNode start = graph.findNode(from);
+        DijkstraNode end = graph.findNode(to);
+        start.setDist(0);
+        pendingNodes.add(start);
+
+        while (!pendingNodes.isEmpty()) {
+            DijkstraNode current = pendingNodes.poll();
+            current.setMark(true);
+
+            if (current == end) {
+                return;
+            }
+
+            for (Edge edge : current.getEdges()) {
+                if (edge.getDest() instanceof DijkstraNode node &&
+                        !node.getMark()) {
+                    double dist = current.getDist() + edge.getWeight();
+
+                    if (!pendingNodes.contains(node) ||
+                            dist < node.getDist()) {
+                        node.setDist(dist);
+                        node.setPrev(current);
+
+                        if (pendingNodes.contains(node)) {
+                            pendingNodes.remove(node);
+                        }
+
+                        pendingNodes.add(node);
+                    }
+                }
+            }
+        }
     }
 
     /**
-    find the route in the graph after applied dijkstra
-    the route should be returned with the start town first
-    */
+     * find the route in the graph after applied dijkstra
+     * the route should be returned with the start town first
+     */
     public List<DijkstraNode> getRoute(Graph<DijkstraNode, Edge> graph, String to) {
         List<DijkstraNode> route = new LinkedList<>();
         DijkstraNode town = graph.findNode(to);
@@ -39,7 +87,9 @@ public class RouteServer implements CommandExecutor {
         List<DijkstraNode> route = getRoute(graph, "Lugano");
         // generate result string
         StringBuilder builder = new StringBuilder();
-        for (DijkstraNode rt : route) builder.append(rt).append("\n");
+        for (DijkstraNode rt : route) {
+            builder.append(rt).append("\n");
+        }
         return builder.toString();
     }
 }