Summary of Union-find algorithm

Not familiar with the Union find algorithm, you can see

http://blog.csdn.net/dm_vincent/article/details/7655764

http://blog.csdn.net/dm_vincent/article/details/7769159

Personally, the blog is very easy to understand, the second link is a few examples of the use of bloggers.

A few questions to consider:

What scenario does this algorithm typically apply to? How to use it?

How do I get the problem to union-find or what is the purpose of the Union?

How to union, that is, two elements to meet what conditions can be union?

>> two meta-related

< P dir= "ltr" style= "LINE-HEIGHT:1.2;MARGIN-TOP:0PT;MARGIN-BOTTOM:0PT;" >	< P dir= "ltr" style= "LINE-HEIGHT:1.2;MARGIN-TOP:0PT;MARGIN-BOTTOM:0PT;" >
Graph Valid Tree	Two vertices of an edge
< P dir= "ltr" style= "LINE-HEIGHT:1.2;MARGIN-TOP:0PT;MARGIN-BOTTOM:0PT;" >		UNION ALL nodes with the specified ID node as the root, summing the value of the elements in the Union
< P dir= "ltr" style= "LINE-HEIGHT:1.2;MARGIN-TOP:0PT;MARGIN-BOTTOM:0PT;" >	Two adjacent 1 elements	union after the union count (by counting the number of root nodes in the Union array)
Surrounded regions	All o elements from the boundary are union together	When the union is finished, those that do not have an O in the bounding box are required to be flipped.

The purpose of union, Graph

Graph Valid Tree

subtree Sum

Number of Islands

https://leetcode.com/problems/surrounded-regions/

This problem debug for a long time, a 20*20 case always pass, because the Oroot rank value is not set large enough,

will be replaced by other elements in the matrix thereby oroot is no longer oroot cause the entire matrix o will be all changed to X.

surrounded Region

Summary of Union-find algorithm