From 241ccd42439621386d3c2a6322cbb9ae1ddb511d Mon Sep 17 00:00:00 2001
From: Jonas Smedegaard <dr@jones.dk>
Date: Sun, 20 Apr 2025 18:22:22 +0200
Subject: include code from course material

---
 com/example/portfolio3/GraphAlgorithms.java | 263 ++++++++++++++++++++++++++++
 1 file changed, 263 insertions(+)
 create mode 100644 com/example/portfolio3/GraphAlgorithms.java

(limited to 'com/example/portfolio3/GraphAlgorithms.java')

diff --git a/com/example/portfolio3/GraphAlgorithms.java b/com/example/portfolio3/GraphAlgorithms.java
new file mode 100644
index 0000000..fdf6def
--- /dev/null
+++ b/com/example/portfolio3/GraphAlgorithms.java
@@ -0,0 +1,263 @@
+import java.io.*;
+import java.util.*;
+
+public class GraphAlgorithms {
+  public static int pathLength(Collection<Edge> edges){
+    // Calculates the length of a path or any other collection of edes
+    // does not require the edges to form a path
+    return edges.stream().mapToInt(e-> e.weight()).sum();
+  }
+
+  public static boolean isPath(List<Edge> edges){
+    // checks whether a list of edges form a path so that
+    // the to-vertex in one edge is the from-vertex of the next
+    for(int i=1;i<edges.size();i++){
+      if(edges.get(i-1).to()!=edges.get(i).from())return false;
+    }
+    return true;
+  }
+
+  public static Integer pathLength(Graph g,List<Vertex> path){
+    //Calculates the length of a path vertices in a graph
+    // return null if vertices are not connected as a path
+    int length=0;
+    for(int i=1;i<path.size();i++){
+      Integer w=g.getWeight(path.get(i-1),path.get(i));
+      if(w==null)return null;
+      length+=w;
+    }
+    return length;
+  }
+
+  //------------------------------------------------------------
+  //
+  //  Comparators and sorting methods
+
+  static int cmpEdgeWeight(Edge e1,Edge e2) {
+    // Comparator of edges based on weight
+    // can be used for sorting a list of edges
+    int w1=e1.weight(),w2=e2.weight();
+    if(w1!=w2)return w1-w2;
+    if(e1.from()!=e2.from())return e1.from().name().compareTo(e2.from().name());
+    return e1.to().name().compareTo(e2.to().name());
+  }
+  static int cmpEdgeFrom(Edge e1,Edge e2) {
+    // Comparator of edges based on from-vertex
+    // can be used for sorting a list of edges
+    if(e1.from()!=e2.from())return e1.from().name().compareTo(e2.from().name());
+    int w1=e1.weight(),w2=e2.weight();
+    if(w1!=w2)return w1-w2;
+    return e1.to().name().compareTo(e2.to().name());
+  }
+  static int cmpEdgeTo(Edge e1,Edge e2) {
+    // Comparator of edges based on from-vertex
+    // can be used for sorting a list of edges
+    if(e1.to()!=e2.to())return e1.to().name().compareTo(e2.to().name());
+    if(e1.from()!=e2.from())return e1.from().name().compareTo(e2.from().name());
+    int w1=e1.weight(),w2=e2.weight();
+    return w1-w2;
+  }
+
+  static List<Edge> sortEdges(Collection<Edge> edges){
+    // sort a collection of edges based on their weights
+    ArrayList<Edge> list=new ArrayList<>(edges);
+    Collections.sort(list,GraphAlgorithms::cmpEdgeWeight);
+    return list;
+  }
+  static List<Edge> sortEdgesFrom(Collection<Edge> edges){
+    // sort a collection of edges based on from-vertex
+    ArrayList<Edge> list=new ArrayList<>(edges);
+    Collections.sort(list,GraphAlgorithms::cmpEdgeFrom);
+    return list;
+  }
+  static List<Edge> sortEdgesTo(Collection<Edge> edges){
+    // sort a collection of edges based on to-vertex
+    ArrayList<Edge> list=new ArrayList<>(edges);
+    Collections.sort(list,GraphAlgorithms::cmpEdgeTo);
+    return list;
+  }
+
+  static List<Vertex> sortVertex(Collection<Vertex> vertices){
+    // sort a collection of vertices based on their name
+    ArrayList<Vertex> list=new ArrayList<>(vertices);
+    Collections.sort(list,(Vertex v1,Vertex v2)-> v1.name().compareTo(v2.name()));
+    return list;
+  }
+
+  //------------------------------------------------------------
+  //
+  //  Algorithms for traverse and minimum spanning tree
+
+  public static Set<Vertex> visitBreadthFirst(Graph g,Vertex v){
+    // traverse a graph depth first from a given vertex
+    // return the set of visited vertices
+    HashSet<Vertex> thisLevel=new HashSet<>();
+    HashSet<Vertex> nextLevel=new HashSet<>();
+    HashSet<Vertex> visited=new HashSet<>();
+    thisLevel.add(v);
+    while(thisLevel.size()>0){
+      System.out.println("level "+thisLevel);
+      for(Vertex w:thisLevel){
+        //System.out.println("visited "+w);
+        visited.add(w);
+        Collection<Edge> outedge=g.outEdge(w);
+        if(outedge==null)continue;
+        for(Edge e: outedge){
+          if(visited.contains(e.to()))continue;
+          if(thisLevel.contains(e.to()))continue;
+          nextLevel.add(e.to());
+        }
+      }
+      thisLevel=nextLevel;
+      nextLevel=new HashSet<Vertex>();
+    }
+    return visited;
+  }
+
+  public static Set<Vertex> visitDepthFirst(Graph g,Vertex v){
+    // traverse a graph depth first from a given vertex
+    // return the set of visited vertices
+    HashSet<Vertex> visit=new HashSet<>();
+    visitDepthFirst(g, v,visit);
+    return visit;
+  }
+
+  private static void visitDepthFirst(Graph g,Vertex v,Set<Vertex> visited){
+    if(visited.contains(v))return;
+    //System.out.println("visited "+v);
+    visited.add(v);
+    for(Edge e: g.outEdge(v))
+      visitDepthFirst(g,e.to(),visited);
+  }
+
+  public static Set<Edge> minimumSpanningTree(Graph g){
+    // an implementation of Prim's algorithm
+    // naive implementation without priorityqueue
+    Collection<Edge> edges=g.edges();
+    HashSet<Edge> mst=new HashSet<>();
+    HashSet<Vertex> frontier=new HashSet<>();
+    for(Edge e:edges){frontier.add(e.from());break;}
+    while(true) {
+      Edge nearest = null;
+      for (Edge e : edges) {
+        if (!frontier.contains(e.from())) continue;
+        if (frontier.contains(e.to())) continue;
+        if (nearest == null || nearest.weight() > e.weight())
+          nearest = e;
+      }
+      if(nearest==null)break;
+      mst.add(nearest);
+      frontier.add(nearest.to());
+    }
+    return mst;
+  }
+
+  public static Set<Edge> dijkstra(Graph g, Vertex start){
+    // returns the tree of shortest paths from start to
+    // all vertices  in the graph
+    // naive implementation without a prorityqueue
+    // create table for done, prev and weight from start
+    int maxint =Integer.MAX_VALUE;
+    HashSet<Vertex> done=new HashSet<>();
+    HashMap<Vertex,Edge> prev=new HashMap<>();
+    HashMap<Vertex,Integer> weight=new HashMap<>();
+    for(Vertex w:g.vertices())weight.put(w,maxint);
+    // start node is done, distance 0 from start
+    weight.put(start,0);
+    done.add(start);
+
+    while(true){
+      // find nearest from a done vertex
+      Vertex nearest = null;
+      int neardist = maxint;
+      Edge done2near=null;
+      for(Vertex w1:done){
+        for (Edge e : g.outEdge(w1)) {
+          Vertex w2 = e.to();
+          if (done.contains(w2)) continue;
+          if ((weight.get(w1) + e.weight()) < neardist) {
+            nearest = e.to();
+            neardist = weight.get(w1) + e.weight();
+            done2near = e;
+          }
+        }
+      }
+      // System.out.println("find nearest "+done2near);
+      // if no more, then we are done
+      if (nearest == null) break;
+        // update distance from this node to other nodes
+      for (Edge e1 : g.outEdge(nearest)) {
+        Vertex w3 = e1.to();
+        int wght = e1.weight();
+        if (weight.get(w3) > (neardist + wght)) {
+          weight.put(w3, neardist + wght);
+        }
+      }
+      done.add(nearest);
+      prev.put(nearest,done2near);
+      weight.put(nearest,neardist);
+    }
+    return new HashSet<Edge>(prev.values());
+  }
+
+  //------------------------------------------------------------
+  //
+  //  IO operations
+
+  public static void readGraph(Graph g, String file) {
+    // read a comma-separated file in the format
+    // stores file as bidirectional graph
+    // <vertex> , <vertex> , <weight>
+    try{
+      BufferedReader in = new BufferedReader(new FileReader(file));
+      for(String line=in.readLine(); line!=null; line=in.readLine()) {
+        if(line.length()==0) continue;
+        String[] arr = line.split(",");
+        if(arr.length!=3) throw new RuntimeException("CSV file format error: "+line);
+        g.insertEdge(arr[0].trim(), arr[1].trim(), Integer.parseInt(arr[2].trim()));
+        g.insertEdge(arr[1].trim(), arr[0].trim(), Integer.parseInt(arr[2].trim()));
+      }
+      in.close();
+    }catch(IOException e){
+      throw new RuntimeException(e);
+    }
+  }
+
+  static void printGraph(Graph g) {
+    for(Vertex v: sortVertex(g.vertices())) {
+      System.out.println(v.toString());
+      for(Edge e:sortEdgesTo(g.outEdge(v)))
+        System.out.println("  "+e.toString());
+    }
+  }
+
+  public static void storeStrings(List<String> list,String f){
+    // store a list of lines as a file
+    try{
+      PrintWriter out=new PrintWriter(new FileWriter(f));
+      for(String s:list){
+        out.println(s);
+      }
+      out.close();
+    }catch(IOException e){
+      throw new RuntimeException(e);
+    }
+  }
+
+  public static ArrayList<String> loadStrings(String f){
+    // read a file a returns a list of lines
+    ArrayList<String> list=new ArrayList<>();
+    try{
+      BufferedReader in=new BufferedReader(new FileReader(f));
+      while(true){
+        String s=in.readLine();
+        if(s==null)break;
+        list.add(s);
+      }
+      in.close();
+    }catch(IOException e){
+      throw new RuntimeException(e);
+    }
+    return list;
+  }
+}
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