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
klmo:
20190424 10:37:57
To check if connected better use optimized DSU than DFS. 

itsshubham_m12:
20190422 17:12:34
Is the graph directed or not??


ll14:
20190315 00:05:27
If you're using Java and has the TLE, please never use Scanner instead of BufferReader 

mynk322:
20190313 10:10:24
Tree is undirected!


haiderbaig:
20190306 10:24:51
Very good introduction to DFS.


knir0103:
20190305 02:51:04
test cases 've been fixed to be undirected Last edit: 20190305 02:51:18 

akashbhalotia:
20190120 11:59:39
AC in java. Simple DSU. Only create DSU if M=N1, else you will get TLE. 

sunny:
20190119 19:16:03
TLE on spoj. Same problem AC on codechef. On codechef time shown is 0.08s taken for AC. WTF!! 

dkkv0000:
20190119 18:38:14
beware graph is directed!!!! Last edit: 20190119 18:38:23 

gaurav_2000:
20190114 15:48:32
GRAPH IS DIRECTED.

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 