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PT07Z - Longest path in a tree |
You are given an unweighted, undirected tree. Write a program to output the length of the longest path (from one node to another) in that tree. The length of a path in this case is number of edges we traverse from source to destination.
Input
The first line of the input file contains one integer N --- number of nodes in the tree (0 < N <= 10000). Next N-1 lines contain N-1 edges of that tree --- Each line contains a pair (u, v) means there is an edge between node u and node v (1 <= u, v <= N).
Output
Print the length of the longest path on one line.
Example
Input: 3 1 2 2 3 Output: 2
| Added by: | Thanh-Vy Hua |
| Date: | 2007-03-28 |
| Time limit: | 0.5s |
| Source limit: | 50000B |
| Memory limit: | 1536MB |
| Cluster: | Cube (Intel G860) |
| Languages: | All except: ERL JS-RHINO NODEJS PERL6 VB.NET |
| Resource: | Co-author Amber |
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2017-12-29 19:39:00
@diptark_bose , you can take node 1 as the starting node for the first dfs (used to calculate the farthest node) as it must be present in every test case , then use farthest node as the starting node for the second dfs. |
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2017-12-29 19:35:15
just calculate the diameter of the tree, diameter-1 is your longest path in the tree |
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2017-12-20 16:40:57
How to decide the initial starting node when doing the 2 bfs approach? |
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2017-12-17 20:19:47
I'm pretty sure there are test cases with 0<=U,V<=N when it says 1<=U,V<=N. faced SIGSEGV (Don't decrease the node no by 1) |
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2017-12-16 07:15:43
AC in one go ! Used 1 dfs. |
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2017-12-02 11:05:04
Applied 2 dfs as well as 2 bfs approach in java..TLE with both approach :(.. Can anyone suggest some optimization techniques as I have analysed memorization can't be applied in this case. |
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2017-10-13 20:47:00 Omar
Run BFS on any node s in the graph, remembering the node u discovered last. Run BFS from u remembering the node v discovered last. d(u,v) is the diameter of the tree. Just make sure to choose the right random node to avoid wrong answer. |
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2017-09-12 11:54:10
It is very hard to not to AC first submission. |
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2017-09-11 15:57:23
#1. Test example on Spoj Toolkit is wrong, it's not even a tree since there is a cycle. Test on your own, 15 1 2 2 3 1 11 3 11 4 11 4 5 5 6 5 7 6 7 4 12 8 12 9 12 8 10 9 10 8 9 Last edit: 2017-09-11 15:57:56 |
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2017-08-25 23:24:24
@sharma96 4 is hardly a valid node index in a tree with only three nodes so your example is invalid input which should not ever happen on spoj |
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