Python bellmanford代码实现
时间: 2023-11-05 14:30:10 浏览: 51
Bellman-Ford算法是一种解决单源最短路径问题的算法,用于处理边权值为负数的情况。以下是Python实现Bellman-Ford算法的代码:
```python
def bellman_ford(graph, start):
# 初始化距离列表,将起点距离设为0,其他距离设为无限大
distances = {node: float('inf') for node in graph}
distances[start] = 0
# 对每个节点进行n-1轮松弛操作
for i in range(len(graph) - 1):
for node in graph:
for neighbor in graph[node]:
# 如果当前节点能到达neighbor节点,且通过当前节点到达neighbor节点的距离小于原来的距离,则更新距离
if distances[node] != float('inf') and distances[node] + graph[node][neighbor] < distances[neighbor]:
distances[neighbor] = distances[node] + graph[node][neighbor]
# 检查是否存在负环
for node in graph:
for neighbor in graph[node]:
if distances[node] != float('inf') and distances[node] + graph[node][neighbor] < distances[neighbor]:
print("该图存在负环,无法求出最短路径")
return None
# 返回起点到各个节点的最短距离
return distances
```
其中,`graph`为图的邻接表表示,`start`为起点。首先将所有节点的距离设为无限大,起点的距离设为0,然后对每个节点进行n-1轮松弛操作,每轮松弛操作都会更新所有节点的最短距离。最后,再检查是否存在负环,如果存在则无法求出最短路径,否则返回起点到各个节点的最短距离。