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
hide comments
lisbecg:
20160415 03:22:32
Did you guys build the graph in order to do DFS? 

sharif ullah:
20160312 12:31:25
just use union find check if there is a loop! 

vimal:
20160306 17:12:11
accepted on codechef... WA here... :D


Neeraj Singh Aithani:
20160216 16:56:15
Actually Test Cases are very weak my solution for


dkumarsingh:
20160122 21:14:52
i am using matrix to represent it's structure as a graph but getting sigsev error 

Aqib Ahmed J:
20160116 06:00:11
Tree doesn't have loops ! Cost me one WA : 

RADHE SHYAM LODHI:
20160112 05:10:29
AC union set 0.00 .. 

dokz:
20160106 06:33:31
Got AC. Just run the single DFS:


Deepak :
20151230 12:34:06
thanks @rahul for your hint 

AASHISH KUMAR:
20151225 10:01:02
AC in one go :) yeyii 
Added by:  ThanhVy Hua 
Date:  20070328 
Time limit:  0.166s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ERL JS 
Resource:  Coauthor Amber 