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
Vaibhav Malik:
20151006 20:54:26
AC in one GO :) 

jarvis:
20150928 23:37:35
First graph :) first DFS :) love it <3 after 5 WA


Sarthak Munshi:
20150925 14:29:21
Check :


[Mayank Pratap]:
20150922 14:16:28
Enjoyed this problem... :)


jyotman94:
20150919 21:03:46
First Graph Problem :) AC 

ram:
20150902 08:35:16
Easy ques :)


tonystark1996:
20150831 15:32:46
Weak Test Cases


coder_shishir:
20150822 23:09:42
awesome problem ..learned a lot !!! 

Vivek:
20150818 10:56:19
if Using DFS, Don't use ADJ Matrix.It would result in O(v^2) time.


SangKuan:
20150812 05:24:18
first i used visited array and got many errors,then is use two hash, colored and merge the edge got ac.no need

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 