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LCA - Lowest Common Ancestor |
A tree is an undirected graph in which any two vertices are connected by exactly one simple path. In other words, any connected graph without cycles is a tree. - Wikipedia
The lowest common ancestor (LCA) is a concept in graph theory and computer science. Let T be a rooted tree with N nodes. The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself). - Wikipedia
Your task in this problem is to find the LCA of any two given nodes v and w in a given tree T.
For example the LCA of nodes 9 and 12 in this tree is the node number 3.
Input
The first line of input will be the number of test cases. Each test case will start with a number N the number of nodes in the tree, 1 <= N <= 1,000. Nodes are numbered from 1 to N. The next N lines each one will start with a number M the number of child nodes of the Nth node, 0 <= M <= 999 followed by M numbers the child nodes of the Nth node. The next line will be a number Q the number of queries you have to answer for the given tree T, 1 <= Q <= 1000. The next Q lines each one will have two number v and w in which you have to find the LCA of v and w in T, 1 <= v, w <= 1,000.
Input will guarantee that there is only one root and no cycles.
Output
For each test case print Q + 1 lines, The first line will have “Case C:” without quotes where C is the case number starting with 1. The next Q lines should be the LCA of the given v and w respectively.
Example
Input: 1 7 3 2 3 4 0 3 5 6 7 0 0 0 0 2 5 7 2 7 Output: Case 1: 3 1
Added by: | hossamyosef |
Date: | 2013-05-13 |
Time limit: | 0.600s-1.113s |
Source limit: | 50000B |
Memory limit: | 1536MB |
Cluster: | Cube (Intel G860) |
Languages: | All |
Resource: | FCIS/ASU Local Contest 2013 |
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2018-06-19 13:35:26
Did Using Euler Tour+RMQ!!! |
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2018-04-14 00:44:12
For those with runtime errors, try setting maxN to something higher than what the problem states. |
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2018-02-02 15:18:50
weak test case ................. no need for using log(N) query |
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2018-01-28 03:18:33
@ipg_2015054 Assume 1 is the root. The problem intends that (in the picture) but doesn't explicitly state it |
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2017-11-16 13:48:33
Can anyone tell me how the edges are undirected , as if they are then we can take any node as the root node and answer will differ according to the root node taken. |
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2017-10-06 09:50:59 Bihan Sen
AC :) Last edit: 2017-10-06 10:16:43 |
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2017-08-18 18:34:30
I got WA because I neglect the 2 points: 1. "...we allow a node to be a descendant of itself..." 2. The edges are undirected. |
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2017-08-09 04:34:56
nani |
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2017-08-05 22:49:50
Weak test case.. |
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2017-07-27 09:04:33
I am getting rte with memory usage of 2000M. Please Help. <snip>. Using lca + rmq(sparse table) Last edit: 2022-09-10 23:24:28 |