CODEWITHSUNDEEP
javaalgorithmshortest-path
user4406103
user4406103

Reputation: 31

Shortest Path Algorithm With Updates

There are N cities and there are M bidirectional roads connected to them , I have to find the shortest path between two fixed cities A and B.

But the problem is there are Q queries given such that path between two cities is blocked , i have to find the shortest path in each Q queries.

My time Complexity in my brute force Algorithm is O(QNlogN) which give me Time Limit Exceeded Error, How can i improve my solution please Help

Pseduo Code:

for u in Q:
  cin>>a>>b;
graph[a][b] = graph[b][a] = INFINITY VALUE
dijkstra algorithm();
cout<<Distance[D]<<endl;

Problem LINK

MY CODE Which Is giving me Time Limit Exceeded Error

Plese Help How can I improve my algorithm ?

Upvotes: 3

Views: 265

Answers (1)

Peter de Rivaz
Peter de Rivaz

Reputation: 33509

The paper Vickrey Prices and Shortest Paths: What is an edge worth? by John Hershberger and Subhash Suri shows how to solve this problem in time O(NlogN+M) where N is the number of vertices, and M is the number of edges.

This allows you to precalculate the M answers depending on which road is blocked, so you can answer each query in O(1), for a total complexity of O(NlogN+M+Q).

Upvotes: 3

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