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Questions tagged [least-common-ancestor]

37 questions
190
votes
34 answers

How to find the lowest common ancestor of two nodes in any binary tree?

The Binary Tree here is may not necessarily be a Binary Search Tree. The structure could be taken as - struct node { int data; struct node *left; struct node *right; }; The maximum solution I could work out with a friend was something…
Siddhant
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Determine least common ancestor at compile-time

There are tons of questions about the least common ancestor algorithm, but this one is different because I'm trying to determine the LCA at compile-time, and my tree is neither binary nor a search tree, even though my simplified version may look…
Nicolas Holthaus
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Lowest Common Ancestor Algorithm

So I have been looking into implementing a lowest common ancestor algorithm. I looked at many different algorithms (mainly variations of Trajan's solution or variations of the RMQ). I am using a non-binary tree. My tree will often change between…
slimbo
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Range Minimum Query approach (from tree to restricted RMQ)

So, I read this TopCoder tutorial on RMQ (Range Minimum Query), and I got a big question. On the section where he introduced the approach, what I can understand until now is this: (The whole approach actually uses methodology introduced in Sparse…
Shane Hsu
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4 answers

How do criss-cross merges arise in Git?

I have been going through the, "git merge-base", man page and I can't understand how multiple merge bases develop. Specifically, I'm hung up on the following illustration in the man page: When the history involves criss-cross merges, there can be…
MACS
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How to finding first common ancestor of a node in a binary tree?

Following is my algorithm to find first common ancestor. But I don’t know how to calculate it time complexity, can anyone help? public Tree commonAncestor(Tree root, Tree p, Tree q) { if (covers(root.left, p) && covers(root.left, q)) …
dojoBeginner
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How to represent a non binary tree and how to do LCA on that tree?

How are non binary trees typically represented? Trees where there is no limit to the number of children a node can have. Is it best to use a Adjacency Matrix or Adjacency List and just assume there will be no cycles, or do something similar to…
drop27
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What are the practical applications of the lowest common ancestor algorithms?

I was having a look at this question and then reading about Tarjan's least common ancestors algorithm. I never came across any applications of LCA algorithms before. Where are such LCA algorithms commonly used?
Lazer
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Find multiple LCAs in unrooted tree

I am trying to implement LCA for unrooted tree. I have given a tree (a connected undirected graph without cycles) and a sequence of queries about LCA for some root and two vertices. Every particular query can have different root, so I cannot use…
ciechowoj
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Why is this implicit cast is not possible?

Given classes and interfaces below, I am wondering why implicit cast: ISomeModelAbstract x = new ConcreteClass(); Is impossible. I tried public interface ISomeModelAbstract where T: IBasicModel But then I cannot use GetById…
Node.JS
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How to compute a least common ancestor algorithm's time complexity?

I came into an article which talking about the LCA algorithms, the code is simple http://leetcode.com/2011/07/lowest-common-ancestor-of-a-binary-tree-part-i.html // Return #nodes that matches P or Q in the subtree. int countMatchesPQ(Node *root,…
bigpotato
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Least common ancestor of multiple nodes in DAG

How can I find a least common ancestors of multiple nodes in a directed acyclic graph? I've found quite a few papers on the topic but they all seem to find LCAs in DAG for two nodes. Are there good algorithms for multiple nodes?
yper
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Finding best common ancestor of two leaf nodes where nodes have zero, one, or two parents

Goal: I am looking for an algorithm to find the best common ancestor of a graph where nodes in the graph can have zero, one, or two parents. I am not sure of the terminology of "best common ancestor": better terminology might be "lowest common…
bgoodr
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LCA problem at interview

Sometimes I come across interview questions like this: "Find the common parent of any 2 nodes in a tree". I noticed that they ask LCA questions also at Google, Amazon, etc. As wikipedia says LCA can be found by intersection of the paths from the…
Michael
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Is there a better way to find lowest common ancestor?

I know similar questions have been asked before, but I think my solution is far simpler. Especially compared to Wikipedia. Please prove me wrong! If you have a tree with nodes that have the given data structure: struct node { node * left; …
theninjagreg
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