Question

我有一个有向，无加权，循环图，并且我想使用python查找给出起点的最长路径。我知道这个问题不能在多项式时间内解决，实际上，上面的解决方案还远远不能解决这个问题。

在这里我发现一些代码，为了适应我的需要我做了一些修改。它可以工作，但会存储我从该源节点传播图形时遇到的每条路径，并最终选择最长的一条，条件是端点是我选择的节点之一。我只想存储符合条件的最长路径，而不是全部存储，那么我想做类似的事情

if islonger and endsWithOutput
   longestpath = currentpath

这可能吗？这是代码：

from collections import defaultdict

def DFS(G,v,seen=None,path=None):
   if seen is None: seen = []
   if path is None: path = [v]

   seen.append(v)

   paths = []
   for t in G[v]:
       if t not in seen:
           t_path = path + [t]
           paths.append(tuple(t_path))
           paths.extend(DFS(G, t, seen[:], t_path))
   return paths


# Define edges
edges = [['1', '3'], ['2', '3'], ['3', '4'], ['4', '6'],['6','5'],['7','5'],
['5','8'],['5','4']]

# Define outputs
outputs = ['8']


# Build graph 
G = defaultdict(list)
for (i,j) in edges:
   G[i].append(j)

# starting from '1'
all_paths = DFS(G, '1') 
max_len   = max(len(p) for p in all_paths if p[-1] in outputs)
max_paths = [p for p in all_paths if len(p) == max_len and p[-1] in outputs]

# Output
print("All Paths:")
print(all_paths)
print("Longest Paths:")
for p in max_paths: print("  ", p)
print("Longest Path Length:")
print(max_len)

使用python在循环图中打印最长的简单路径

0 个答案: