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
hide comments
hackerakhil:
2021-02-04 11:57:45
https://www.spoj.com/submit/LCA/id=27389011
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harshiscoding:
2021-01-23 15:13:42
@up_in_smoke ,use if(n===0) break |
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princemishra:
2020-12-31 18:35:09
even LCA with O(n) works and rooted at node 1 Last edit: 2020-12-31 18:35:33 |
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satyamkr118:
2020-12-27 12:35:12
My 100th one!! |
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raka143:
2020-08-28 14:12:59
LCA using binary lifting works fine. Took me 0.05s. |
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k_r_i_s_h_123:
2020-08-24 15:03:35
getting wrong answer using binary lifting .............HELP
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junloveyin:
2020-08-22 16:03:42
@sknayak you should reset array after found all LCA of (u,v) . Last edit: 2020-08-22 16:04:02 |
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sknayak:
2020-08-20 09:27:44
I am getting TLE using binary lifting and sparse table in c++. Can anyone help please? |
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up_in_smoke:
2020-08-10 14:43:50
I am getting this error : runtime error (SIGABRT) and I've no idea how please help. Used RMQ + segment tree
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csq31:
2020-08-06 18:45:41
rmb to swap(tin[u],tin[v]) when querying using rmq else you might get segfault |
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 |