Tutor All Students

You are given a number of students and a set of tutoring sessions. Each session covers a continuous range of students. The goal is to determine if it is possible to cover all the students, from student 1 to student N, using one or more of the provided sessions.

For each test case, you are provided with:

• N: The total number of students.
• M: The total number of tutoring sessions available.
• A list of M sessions, where each session is described by two integers A and B (with \(1 \leq A \leq B \leq N\)). A session covers all students numbered from A to B (inclusive).

Your task is to decide whether the union of selected sessions can form a continuous cover of the range \([1, N]\). If they can, print YES; otherwise, print NO for that test case.

Note: Sessions may overlap and can be used in combination. The solution should use a greedy strategy to choose sessions that extend the current coverage as far as possible.

inputFormat

The input is given from standard input (stdin) and has the following format:

T
N1 M1
A11 B11
A12 B12
... 
A1M1 B1M1
N2 M2
A21 B21
... 
A2M2 B2M2
...

Here, T is the number of test cases. For each test case, the first line contains two integers N and M. The next M lines contain two integers each representing the range [A, B] of a tutoring session.

outputFormat

For each test case, output a single line containing either YES if it is possible to cover all students from 1 to N using the given sessions, or NO if it is not.

## sample

1
5 3
1 2
2 4
3 5

YES

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