題干：

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

Sample Input

2 3 3 3 1 2 3 2 1 2 1 1 3 3 2 1 3 2 1 3 1 1

Sample Output

YES NO

題目大意：

題目大意：

一共有N個學生跟P門課程,一個學生可以任意選一?門或多門課,問是否達成:?

? 1.每個學生選的都是不同的課(即不能有兩個學生選同一門課)

? 2.每門課都有一個代表(即P門課都被成功選過)

輸入為:

第一行一個T代表T組數據

P N(P課程數, N學生數)

接著P行：

第幾行代表第幾門課程，首先是一個數字k代表對這門課程感興趣的同學的個數，接下來是k個對這門課程感興趣同學的編號。

輸出為:

若能滿足上面兩個要求這輸出”YES”,否則為”NO”

注意：是課程匹配的學生，學生沒課上沒事.....

解題報告：

? ?二分圖模板，連建圖都不需要，，，不解釋了

AC代碼：

#include<bits/stdc++.h> using namespace std; int maze[305][305],nxt[305]; bool used[305]; int p,n,m; bool find(int x) {for(int i = 1; i<=n; i++) {if(maze[x][i] && used[i] == 0) {used[i] = 1;if(nxt[i] == 0 || find(nxt[i])) {nxt[i] = x;return 1;}}}return 0 ; }int main() {int t,tmp;cin>>t;while(t--) {memset(maze,0,sizeof maze);memset(nxt,0,sizeof nxt);scanf("%d%d",&p,&n);for(int i = 1; i<=p; i++) {scanf("%d",&m);while(m--) {scanf("%d",&tmp);maze[i][tmp] = 1;}}int ans = 0;for(int i = 1; i<=p; i++) {memset(used,0,sizeof used);if(find(i)) ans++;}if(ans == p) puts("YES");else puts("NO");} return 0; }

?

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