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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KEVALSAHU:
20131230 05:22:25
simple problem guys :) Last edit: 20120826 01:14:34 

:
20120621 09:40:19
Last edit: 20140227 08:09:25 

Diego Guapo Mendieta:
20120501 18:51:58
give me the solution :D 

tracy filbert ridwan:
20111104 06:11:52
just a simple flood fill :D 

pavan:
20110722 17:55:06
weak test cases 

albertg:
20110424 10:33:39
NO 

kiransk:
20110422 04:44:35
is the input graph connected? 

albertg:
20110419 07:03:38
YES. THAT'S RIGHT. 

:D:
20110117 21:45:39
One test case per file. 
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 