Data update

Task/Dijkstras-algorithm/PascalABC.NET/dijkstras-algorithm.pas

@@ -0,0 +1,78 @@
+type
+  Edge = auto class
+    start, &end: char;
+    cost: real;
+  end;
+
+  Graph = auto class
+    edges: array of Edge;
+    vertices: HashSet<char>;
+
+    constructor(params edges: array of (char, char, real));
+    begin
+      Self.edges := edges.Select(e -> new Edge(e[0], e[1], e[2])).ToArray;
+      Self.vertices := new HashSet<char>(
+        Self.edges.Select(e -> e.start) + Self.edges.Select(e -> e.end)
+      );
+    end;
+
+    function Dijkstra(source, dest: char): sequence of char;
+    begin
+      assert(vertices.Contains(source));
+
+      var inf := real.MaxValue;
+      var dist := Dict(vertices.Select(v -> (v, inf)));
+      var previous := Dict(vertices.Select(v -> (v, ' ')));
+      dist[source] := 0;
+
+      var q := vertices.ToHashSet;
+      var neighbours := Dict(vertices.Select(v -> (v, new HashSet<(char, real)>)));
+
+      foreach var edge in edges do
+      begin
+        neighbours[edge.start].Add((edge.end, edge.cost));
+        neighbours[edge.end].Add((edge.start, edge.cost));
+      end;
+
+      while q.Count > 0 do
+      begin
+        var u := q.MinBy(v -> dist[v]);
+        q.Remove(u);
+
+        if (dist[u] = inf) or (u = dest) then
+          break;
+
+        foreach var (v, cost) in neighbours[u] do
+        begin
+          var alt := dist[u] + cost;
+          if alt < dist[v] then
+          begin
+            dist[v] := alt;
+            previous[v] := u;
+          end;
+        end;
+      end;
+
+      var s := new List<char>;
+      var u := dest;
+
+      while previous[u] <> ' ' do
+      begin
+        s.Insert(0, u);
+        u := previous[u];
+      end;
+
+      s.Insert(0, u);
+      Result := s;
+    end;
+  end;
+
+begin
+  var gr := new Graph(
+    ('a', 'b', 7.0), ('a', 'c', 9.0), ('a', 'f', 14.0),
+    ('b', 'c', 10.0), ('b', 'd', 15.0), ('c', 'd', 11.0),
+    ('c', 'f', 2.0), ('d', 'e', 6.0), ('e', 'f', 9.0)
+  );
+
+  gr.Dijkstra('a', 'e').Println;
+end.