Courses

Time Limit: 10 Seconds
Memory Limit: 32768 KB

Consider a group of N students and P courses. Each student visits zero, one
or more than one courses. Your task is to determine whether it is possible to
form a committee of exactly P students that satisfies simultaneously the conditions:

. every student in the committee represents a different course (a student can
represent a course if he/she visits that course)

. each course has a representative in the committee

Your program should read sets of data from a text file. The first line of the
input file contains the number of the data sets. Each data set is presented
in the following format:

P N

Count1 Student1 1 Student1 2 ... Student1 Count1

Count2 Student2 1 Student2 2 ... Student2 Count2

......

CountP StudentP 1 StudentP 2 ... StudentP CountP

The first line in each data set contains two positive integers separated by
one blank: P (1 <= P <= 100) - the number of courses and N (1 <= N <= 300) - the number
of students. The next P lines describe in sequence of the courses . from course
1 to course P, each line describing a course. The description of course i is
a line that starts with an integer Count i (0 <= Count i <= N) representing
the number of students visiting course i. Next, after a blank, you��ll find the
Count i students, visiting the course, each two consecutive separated by one
blank. Students are numbered with the positive integers from 1 to N.

There are no blank lines between consecutive sets of data. Input data are correct.

The result of the program is on the standard output. For each input data set
the program prints on a single line ��YES�� if it is possible to form a committee
and ��NO�� otherwise. There should not be any leading blanks at the start of the
line.

An example of program input and output:

**Input**

2

3 3

3 1 2 3

2 1 2

1 1

3 3

2 1 3

2 1 3

1 1

**Output**

YES

NO

Source:

**Southeastern Europe 2000**
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