Mother Vertex
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  Difficulty: Easy   Marks: 2

Find the Mother vertex in a directed graph. A mother vertex in a graph G = (V,E) is a vertex v such that all other vertices in G can be reached by a path from v.

Input:
The first line of input contains an integer T. Then T test cases follow. Each test case contains two integers N and M. In the next line are M space separated values u,v denoting an edge from u to v.

Output: For each testcase return the mother vertex of graph (if existes) else return -1.

Note: This is a functional probem. Complete function findmother().

Constraints:
1 <= T <= 100
1 <= N, M <= 104
1 <= u, v <= N

Example:
Input:

2
5 5
1 0 0 2 2 1 0 3 3 4
3 2
0 1 2 1

Ouput:
0
-1

Explanation:
Testcase 1:
According to the given edges, all nodes can be reaced from nodes from 0, 1 and 2. But, since we are traversing from node 0, so 0 is the output.

Testcase 2: According to the given edges, no vertices are there from where we can reach all vertices. So, output is -1.

 

** For More Input/Output Examples Use 'Expected Output' option **

Author: SIDG


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