Courses

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

23 33 1 2 32 1 21 13 32 1 32 1 31 1

Output

YESNO 

Sample Input

23 33 1 2 32 1 21 13 32 1 32 1 31 1

Sample Output

YESNO 

题意：

一共有P门课程，N名学生，每名学生可以选任意多门课程，但不能选两门一样的课程

是否可以达成：

  1.每个学生选的都是不同的课(即不能有两个学生选同一门课)

  2.每门课都有一个代表(即P门课都被成功选过)

输入：

第一行测试样例数T

每个测试样例先输入P,N

以下P行，先输入一个数k,表示共K人对这门课感兴趣，之后K个数表示学生编号

代码：

#include<stdio.h>#include<string.h>#include<vector>using namespace std;const int N = 305;const int P = 105;int n,m;int e[P][N];int match[N],used[N];int Find(int x){    //找X的匹配for(int i=1;i<=m;i++){if(e[x][i]&&!used[i]){used[i]=1;if(match[i]==-1||Find(match[i])){match[i]=x;return 1;}}}return 0;}int hungary(){int ans=0;memset(match,-1,sizeof(match));for(int i=1;i<=n;i++){memset(used,0,sizeof(used));if(Find(i)) ans++;}return ans;}int main(){int T;scanf("%d",&T);while(T--){memset(e,0,sizeof(e));scanf("%d%d",&n,&m);for(int i=1;i<=n;i++){int k;scanf("%d",&k);for(int j=0;j<k;j++){int a;scanf("%d",&a);e[i][a]=1;}}if(hungary()==n) printf("YES\n");else printf("NO\n");}return 0;}