PT07Y  Is it a tree
You are given an unweighted, undirected graph. Write a program to check if it's a tree topology.
Input
The first line of the input file contains two integers N and M  number of nodes and number of edges in the graph (0 < N <= 10000, 0 <= M <= 20000). Next M lines contain M edges of that graph  Each line contains a pair (u, v) means there is an edge between node u and node v (1 <= u,v <= N).
Output
Print YES if the given graph is a tree, otherwise print NO.
Example
Input: 3 2 1 2 2 3 Output: YES
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artistic_15:
20181229 20:05:48
Easy Union Find Implementation. 

suyashky:
20181127 08:40:39
learned a lot....good question for beginners.


sudhanshu751:
20181028 21:12:31
Last edit: 20181029 18:12:57 

sudhanshu751:
20181028 21:09:15
Last edit: 20181028 21:13:25 

themast3r:
20180922 18:44:52
Simple Disjoint Set Union gets AC! 

harry_shit:
20180919 12:54:03
can someone tell me what will be the start node.is it 1?? 

phoemur:
20180912 00:58:36
Beware Adjacency Matrix will most likely TLE.


frpartho:
20180728 22:34:31
simple dfs. increment a counter on dfs function. if counter > node*node then there is a cycle.


rohitnarayan:
20180624 23:04:46
Simple DFS!! 

mayank1208_:
20180621 23:03:31
got two WA due..to yes instead of YES....finally AC 
Added by:  ThanhVy Hua 
Date:  20070328 
Time limit:  0.5s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ERL JSRHINO 
Resource:  Coauthor Amber 