diff --git a/problems/kamacoder/0095.城市间货物运输II.md b/problems/kamacoder/0095.城市间货物运输II.md index ac6ccf3c..a88e462a 100644 --- a/problems/kamacoder/0095.城市间货物运输II.md +++ b/problems/kamacoder/0095.城市间货物运输II.md @@ -333,6 +333,8 @@ public class Main { ### Python +Bellman-Ford方法求解含有负回路的最短路问题 + ```python import sys @@ -388,6 +390,52 @@ if __name__ == "__main__": ``` +SPFA方法求解含有负回路的最短路问题 + +```python +from collections import deque +from math import inf + +def main(): + n, m = [int(i) for i in input().split()] + graph = [[] for _ in range(n+1)] + min_dist = [inf for _ in range(n+1)] + count = [0 for _ in range(n+1)] # 记录节点加入队列的次数 + for _ in range(m): + s, t, v = [int(i) for i in input().split()] + graph[s].append([t, v]) + + min_dist[1] = 0 # 初始化 + count[1] = 1 + d = deque([1]) + flag = False + + while d: # 主循环 + cur_node = d.popleft() + for next_node, val in graph[cur_node]: + if min_dist[next_node] > min_dist[cur_node] + val: + min_dist[next_node] = min_dist[cur_node] + val + count[next_node] += 1 + if next_node not in d: + d.append(next_node) + if count[next_node] == n: # 如果某个点松弛了n次,说明有负回路 + flag = True + if flag: + break + + if flag: + print("circle") + else: + if min_dist[-1] == inf: + print("unconnected") + else: + print(min_dist[-1]) + + +if __name__ == "__main__": + main() +``` + ### Go ### Rust