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
wewark:
20160808 20:17:51
toolkit gives wrong answers, don't use it 

karan_mirani:
20160807 13:53:11
Do NOT use spoj toolkit for this one! 

square1001:
20160726 05:46:46
I used unionfind tree and I got 0.00 sec! 

adichd123:
20160712 13:58:54
I guess the test cases are weak.My naive solution also got accepted. 

Murad Al Wajed:
20160705 13:57:08
nice graph problem for biggener 

geeta:
20160702 22:36:02
Easy!!! did using BFS!!!


KD :
20160628 20:26:21
DSU rocks!!!!! 

ajay_raj:
20160625 19:18:37
Last edit: 20160701 03:48:29 

baadshah_:
20160622 11:19:46
tree should have edges n1


sam96:
20160610 18:18:03
HINT : A graph is a cycle if it no. of connected components=1 and edges = nodes1

Added by:  ThanhVy Hua 
Date:  20070328 
Time limit:  0.166s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ERL JSRHINO 
Resource:  Coauthor Amber 