Data commit

Task/Dijkstras-algorithm/Python/dijkstras-algorithm.py

@@ -0,0 +1,50 @@
+from collections import namedtuple, deque
+from pprint import pprint as pp
+
+
+inf = float('inf')
+Edge = namedtuple('Edge', ['start', 'end', 'cost'])
+
+class Graph():
+    def __init__(self, edges):
+        self.edges = [Edge(*edge) for edge in edges]
+        # print(dir(self.edges[0]))
+        self.vertices = {e.start for e in self.edges} | {e.end for e in self.edges}
+
+    def dijkstra(self, source, dest):
+        assert source in self.vertices
+        dist = {vertex: inf for vertex in self.vertices}
+        previous = {vertex: None for vertex in self.vertices}
+        dist[source] = 0
+        q = self.vertices.copy()
+        neighbours = {vertex: set() for vertex in self.vertices}
+        for start, end, cost in self.edges:
+            neighbours[start].add((end, cost))
+            neighbours[end].add((start, cost))
+
+        #pp(neighbours)
+
+        while q:
+            # pp(q)
+            u = min(q, key=lambda vertex: dist[vertex])
+            q.remove(u)
+            if dist[u] == inf or u == dest:
+                break
+            for v, cost in neighbours[u]:
+                alt = dist[u] + cost
+                if alt < dist[v]:                                  # Relax (u,v,a)
+                    dist[v] = alt
+                    previous[v] = u
+        #pp(previous)
+        s, u = deque(), dest
+        while previous[u]:
+            s.appendleft(u)
+            u = previous[u]
+        s.appendleft(u)
+        return s
+
+
+graph = Graph([("a", "b", 7),  ("a", "c", 9),  ("a", "f", 14), ("b", "c", 10),
+               ("b", "d", 15), ("c", "d", 11), ("c", "f", 2),  ("d", "e", 6),
+               ("e", "f", 9)])
+pp(graph.dijkstra("a", "e"))