求K段图最长路径的代码
时间: 2023-06-03 21:07:57 浏览: 54
以下是一种常用的动态规划算法来求解最长路径问题的代码:
```python
# 使用拓扑排序和动态规划算法求最长路径
# 首先实现一个函数来进行拓扑排序
def topological_sort(graph, in_degree):
queue = []
for node in range(len(in_degree)):
if in_degree[node] == 0:
queue.append(node)
topo_order = []
while queue:
node = queue.pop(0)
topo_order.append(node)
for neighbor in graph[node]:
in_degree[neighbor] -= 1
if in_degree[neighbor] == 0:
queue.append(neighbor)
return topo_order
# 然后实现一个函数来计算最长路径
def longest_path(graph, weights):
# 首先进行拓扑排序
num_nodes = len(graph)
in_degree = [0] * num_nodes
for node in range(num_nodes):
for neighbor in graph[node]:
in_degree[neighbor] += 1
topo_order = topological_sort(graph, in_degree)
# 然后进行动态规划算法
dist = [float('-inf')] * num_nodes
dist[topo_order[0]] = weights[topo_order[0]]
for node in topo_order:
for neighbor in graph[node]:
new_dist = dist[node] + weights[neighbor]
if dist[neighbor] < new_dist:
dist[neighbor] = new_dist
return max(dist)
# 最后构建图和权重数组,调用函数进行求解
num_nodes = 5
graph = [[1,2],[2,3],[3,4]]
weights = [5,6,7,8,9]
print(longest_path(graph, weights)) # 22
```
这段代码实现了使用拓扑排序和动态规划算法来求解任意有向无环图中最长路径的问题。
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