add: Bellman-Ford

chapter12/5_bellman-ford.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+# coding=utf-8
+
+#######################################################################################
+# Bellman-Ford 单源最短路径算法
+#######################################################################################
+from typing import Dict
+
+
+def bellmanFord(distances: Dict, origin: str):
+    # edges => 用来存放所有的边
+    # result => 用来存放最短距离的映射结果
+    edges, result = [], {}
+    for node, neighbours in distances.items():
+        for neighbour, weight in neighbours.items():
+            edges.append((node, neighbour, weight))
+        result[node] = float('inf')
+    result[origin] = 0
+
+    # 每轮都使用所有的边对节点进行松弛操作，最多运行n-1轮
+    for i in range(len(distances) - 1):
+        for u, v, w in edges:
+            if result[v] > result[u] + w:
+                result[v] = result[u] + w
+    return result
+
+
+if __name__ == '__main__':
+    distances = {
+        'A': {'C': 4, 'B': 2},
+        'B': {'A': 1, 'G': 1},
+        'C': {'B': -3, 'G': 1},
+        'G': {}
+    }
+    print(bellmanFord(distances, 'A'))