DAG 中最长的总路径

问题描述

我试图在图中找到任意两对顶点之间存在的最长整体路径。我写了这段代码来从源顶点返回最长的路径。但我不知道如何更改它，以便它为我提供任何一对顶点之间最长的整体路径？如果有帮助，我的图表将具有单位权重，因此我不关心负权重。

def topologicalSortUtil(v):
    global Stack,visited,adj
    visited[v] = True
 
    # Recur for all the vertices adjacent to this vertex
    # list<AdjListNode>::iterator i
    for i in adj[v]:
        if (not visited[i[0]]):
            topologicalSortUtil(i[0])
 
    # Push current vertex to stack which stores topological
    # sort
    Stack.append(v)
 
# The function to find longest distances from a given vertex.
# It uses recursive topologicalSortUtil() to get topological
# sorting.
def longestPath(s):
    global Stack,adj,V
    dist = [-10**9 for i in range(V)]
 
    # Call the recursive helper function to store Topological
    # Sort starting from all vertices one by one
    for i in range(V):
        if (visited[i] == False):
            topologicalSortUtil(i)
    # print(Stack)
 
    # Initialize distances to all vertices as infinite and
    # distance to source as 0
    dist[s] = 0
    # Stack.append(1)
 
    # Process vertices in topological order
    while (len(Stack) > 0):
       
        # Get the next vertex from topological order
        u = Stack[-1]
        del Stack[-1]
        #print(u)
 
        # Update distances of all adjacent vertices
        # list<AdjListNode>::iterator i
        if (dist[u] != 10**9):
            for i in adj[u]:
                # print(u,i)
                if (dist[i[0]] < dist[u] + i[1]):
                    dist[i[0]] = dist[u] + i[1]
 
    # Prthe calculated longest distances
    # print(dist)
    for i in range(V):
        print("INF ",end="") if (dist[i] == -10**9) else print(dist[i],end=" ")
 
# Driver code
if __name__ == '__main__':
    V,Stack,visited = 6,[],[False for i in range(7)]
    adj = [[] for i in range(7)]
     
    # Create a graph given in the above diagram.
    # Here vertex numbers are 0,1,2,3,4,5 with
    # following mappings:
    # 0=r,1=s,2=t,3=x,4=y,5=z
    adj[0].append([1,5])
    adj[0].append([2,3])
    adj[1].append([3,6])
    adj[1].append([2,2])
    adj[2].append([4,4])
    adj[2].append([5,2])
    adj[2].append([3,7])
    adj[3].append([5,1])
    adj[3].append([4,-1])
    adj[4].append([5,-2])
 
    s = 1
    print("Following are longest distances from source vertex ",s)
    longestPath(s)```

解决方法

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