{"trustable":true,"prependHtml":"\u003cscript\u003e\n window.katexOptions \u003d {\n delimiters: [\n {left: \u0027\\\\(\u0027, right: \u0027\\\\)\u0027, display: false},\n ]\n };\n\u003c/script\u003e\n","sections":[{"title":"","value":{"format":"MD","content":"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:\n\n- every student in the committee represents a different course (a student can represent a course if he/she visits that course)\n\n- each course has a representative in the committee\n\nYour 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:\n\n```\nP N\nCount1 Student1 1 Student1 2... Student1 Count1\nCount2 Student2 1 Student2 2... Student2 Count2\n......\nCountP StudentP 1 StudentP 2... StudentP CountP\n```\n\nThe first line in each data set contains two positive integers separated by one blank: P (1 \u0026lt;\u003d P \u0026lt;\u003d 100) - the number of courses and N (1 \u0026lt;\u003d N \u0026lt;\u003d 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 \u0026lt;\u003d Count i \u0026lt;\u003d N) representing the number of students visiting course i. Next, after a blank, youll 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.\n\nThere are no blank lines between consecutive sets of data. Input data are correct.\n\nThe 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.\n\n### Example Input\n\n```in\n2\n3 3\n3 1 2 3\n2 1 2\n1 1\n3 3\n2 1 3\n2 1 3\n1 1\n```\n\n### Example Output\n\n```out\nYES\nNO\n```\n"}}]}