SPOJ.com - Problem PT07Y

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

Submit solution!

Added by:	Thanh-Vy Hua
Date:	2007-03-28
Time limit:	0.5s
Source limit:	50000B
Memory limit:	1536MB
Cluster:	Cube (Intel G860)
Languages:	All except: ERL JS-RHINO
Resource:	Co-author Amber

hide comments

2017-02-25 21:50:09
should be moved to tutorial,

2017-02-13 17:15:02
4 hours in front of PC,2 hours of testing,1 hour of No and then Green Tick <3 .

2017-02-13 09:08:47
beautiful solution using union-find

2017-02-12 13:57:13
Weak test cases. Admin, please check the test cases once again.

Last edit: 2017-02-12 13:57:37

2017-02-10 17:45:00
IMO it's easier to code using union-find than BFS/DFS, since you don't even need to keep the edges in memory.

2016-12-23 07:28:04
Spoilers:
1.Graph should be connected.
2.No of cycles in graph == 0.
3.No of edges == No of nodes - 1.
Note : Use adjacency list and **STL .

2016-12-20 08:33:04
Use the fact that a tree has n-1 edges and DFS from one node visits all the nodes........green in first go;)

2016-12-19 18:16:48
use adjacency list instead of adjacency matrix @reconnect as v*v>>e i.e. it will be sparse matrix.lead to waste of time on traversing.

2016-12-19 08:39:33
did it using simple bfs!! first graph problem :] (out of the world feeling :D)

2016-12-13 15:29:11
Check the condition of N = 1