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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sa03195100:
20200218 11:58:55
2


prithvi_3d2y:
20200206 16:14:54
SImple AC:


sangmai:
20200116 11:57:27
dfs with recursion gets TLE, use queue instead 

i_master:
20191230 23:00:07
Just think about it conceptually. What is a tree? A tree is a connected undirected acyclic graph.


karandeep09:
20191230 16:38:25
AC


r15habhgup11:
20191105 11:46:00
Can someone plzz tell me answer of this case and why


invincibel:
20190923 08:40:58
use unionfind much better for this problem 

mriow:
20190821 07:55:05
HINT:


ashishgh1997:
20190817 08:05:37
The tree may not be a binary tree. A node may have more than 3 childs 

nayeem_joy:
20190810 15:17:34
two cases should be handled here , if u feel struggle

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 