Bellman-Ford algorithm

Author: ivanmmarkovic

graphs/bellman–ford/graph.py

@@ -0,0 +1,47 @@
+
+#  Bellman-Ford algorithm
+#  Find shortest paths from one vertex,
+#  to all other vertices in weighted graph.
+#  Runtime O(V*E)
+
+class Graph:
+    def __init__(self):
+        self.vertices: list = []
+        self.edges: list = []
+        self.distance: dict = {}
+        self.prev: dict = {}
+
+    def add_vertex(self, label: str):
+        self.vertices.append(label)
+        self.distance[label] = None
+        self.prev[label] = None
+
+    def add_edge(self, label1: str, label2: str, weight: int):
+        self.edges.append([label1, label2, weight])
+
+    def bellman_ford(self, source: str):
+        self.distance[source] = 0
+
+        for _ in range(len(self.vertices)):
+
+            for edge in self.edges:
+                label1: str = edge[0]
+                label2: str = edge[1]
+                weight: int = edge[2]
+
+                if self.distance[label1] is None:
+                    continue
+                if self.distance[label2] is None:
+                    self.distance[label2] = self.distance[label1] + weight
+                    self.prev[label2] = label1
+                    continue
+                if self.distance[label1] + weight < self.distance[label2]:
+                    self.distance[label2] = self.distance[label1] + weight
+                    self.prev[label2] = label1
+                    continue
+
+    def print_distances(self, source: str):
+        for v in self.vertices:
+            if v != source:
+                distance: int = self.distance[v]
+                print(f'Distance from {source} to {v} is {distance}')