Detecting Cycles in a Directed Graph

You are given a directed graph with \(N\) vertices and \(M\) edges. Your task is to determine whether the graph contains a cycle. A cycle is defined as a non-empty sequence of edges \( (v_1, v_2), (v_2, v_3), \dots, (v_k, v_1) \) where \(k \ge 1\), meaning that there is a path that starts and ends at the same vertex.

If the graph contains at least one cycle, print YES; otherwise, print NO.

inputFormat

The first line of input contains a single integer \(T\) (the number of test cases). Each test case is described as follows:

• The first line contains two space-separated integers \(N\) and \(M\) representing the number of vertices and edges respectively.
• The next \(M\) lines each contain two space-separated integers \(u\) and \(v\) denoting a directed edge from vertex \(u\) to vertex \(v\).

It is guaranteed that \(1 \leq u, v \leq N\).

outputFormat

For each test case, output a single line containing either YES if the graph contains a cycle, or NO otherwise.

## sample

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

YES
NO
YES
NO

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