## 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
 jyotman94: 2015-09-19 21:03:46 First Graph Problem :) AC ram: 2015-09-02 08:35:16 Easy ques :) My first graph problem. AC in one go. :) :) tonystark1996: 2015-08-31 15:32:46 Weak Test Cases 4 2 1 2 3 4 Answer is NO But my code gives YES,still code accepted coder_shishir: 2015-08-22 23:09:42 awesome problem ..learned a lot !!! Vivek: 2015-08-18 10:56:19 if Using DFS, Don't use ADJ Matrix.It would result in O(v^2) time. Go for DFS+ ADJList. With Matrix,got TLE, With List Accepted. SangKuan: 2015-08-12 05:24:18 first i used visited array and got many errors,then is use two hash, colored and merge the edge got ac.no need dfs or bfs, but i think union find is the best way Last edit: 2015-08-12 05:24:51 nadavishe: 2015-08-10 15:48:19 Very week test cases Saksham : 2015-08-04 01:50:59 no need of graph harkirat: 2015-07-28 13:52:53 how weak are the test cases? My solution is completely wrong but got ac! Anurag Pasi: 2015-07-05 18:13:25 @Tanmay Kulshrestha I partially agree with u, when m==n-1 and still not a tree i.e it is cyclic , but i dont think there will b a totally disconnected node mayb there or mayb not u cant say.. i hope this helps

 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