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
Added by:  ThanhVy Hua 
Date:  20070328 
Time limit:  0.166s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel Pentium G860 3GHz) 
Languages:  All except: ERL JS SCM chicken 
Resource:  Coauthor Amber 
hide comments
arkro:
20140920 06:52:50
Got a lot of WA for writing "yes" and "no". Finally AC! :P 

Dhruv Raj Singh Rathore:
20140905 11:05:13
what if graph is disjoint and separately both of them form a tree


Brij Vaid:
20140824 20:32:36
how to solve without dfs?


do_do:
20140822 08:07:26
unionfind algorithm worked... :) 

anand pandey:
20140816 01:59:11
Last edit: 20140816 14:30:58 

anand pandey:
20140816 01:58:44
[code removed by cyclops; see notes below, "1. Don't post any source code here."] Last edit: 20140816 04:21:23 

Naruto uzumaki:
20140815 18:39:13
@jarvis this is a tree, 

Miroslav Kovar:
20140812 20:40:11
Please, what are some tricky test cases? I am getting WA, although the algorithm works fine for everything I come up with... 

.:: Jarv1s ::.:
20140810 00:50:28
4 3


mohsin mohammad:
20140806 16:37:56
My first graph problem AC in first attempt
