lecture 8

SoSe24/lec06_graph/mst.py

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+import math
+import re
+from graph import Graph, AdjacencyListGraph, AdjacencyMatrixGraph, NodeColor, Vertex
+import heapq
+
+
+def mst_prim(self, start_name: str = None):
+
+    distance_map = {}
+    parent_map = {}
+
+    Vertex.__lt__ = lambda self, other: distance_map[self] < distance_map[other]
+
+    queue = []
+
+    if start_name is None:
+        start_name = self.all_vertices()[0].value;
+
+    # Initialize the maps
+    for vertex in self.all_vertices():
+        distance_map[vertex] = 0 if vertex.value == start_name else math.inf
+        parent_map[vertex] = None
+        heapq.heappush(queue, vertex)
+
+    # Process the queue
+    cost = 0
+    while len(queue) > 0:
+        vertex = heapq.heappop(queue)
+        cost += distance_map[vertex]
+        for (dest, w) in self.get_adjacent_vertices_with_weight(vertex.value):
+            if dest in queue and distance_map[dest] > w:
+                queue.remove(dest)
+                distance_map[dest] = w
+                parent_map[dest] = vertex
+                heapq.heappush(queue, dest)
+
+    # Return the distance and predecessor maps
+    return parent_map, cost
+
+AdjacencyListGraph.mst_prim = mst_prim
+AdjacencyMatrixGraph.mst_prim = mst_prim
+
+
+def read_elektro_into_graph(graph: Graph, filename: str):
+    pattern = re.compile(r'"([^"]+)";"([^"]+)";(\d+)')
+    with (open(filename, "r") as file):
+        for line in file:
+            m = pattern.match(line)
+            if m:
+                start_name = m.group(1)
+                end_name = m.group(2)
+                cost = int(m.group(3))
+                graph.insert_vertex(start_name)
+                graph.insert_vertex(end_name)
+                graph.connect(start_name, end_name, cost)
+                graph.connect(end_name, start_name, cost)
+
+if __name__ == "__main__":
+
+    graph = AdjacencyMatrixGraph()
+    read_elektro_into_graph(graph, "../../elektro.txt")
+    parents, cost = graph.mst_prim()
+    print(f"Kosten {cost}")
+    for node, parent in parents.items():
+        if parent is not None:
+            print(f"{node} - {parent}")

elektro.txt

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+"Höhleneingang";"Ost/West-Passage";5
+"Höhleneingang";"Nord/Süd-Passage";3
+"Nord/Süd-Passage";"Nebelraum";7
+"Steiniger Pfad";"Ost/West-Passage";2
+"Ost/West-Passage";"Schwefelgewölbe";4
+"Schwefelgewölbe";"Steiniger Pfad";1
+"Schatzkammer";"Nebelraum";2
+"Steiniger Pfad";"Schatzkammer";6