HDU 1083 COURSES 【二分图最大匹配】

Description

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 
  

Input

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

P N 
Count1 Student _{1 1} Student _{1 2} ... Student _{1 Count1} 
Count2 Student _{2 1} Student _{2 2} ... Student _{2 Count2} 
... 
CountP Student _{P 1} Student _{P 2} ... Student _{P 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抣l 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. 

Output

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.

Sample Input

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

Sample Output

YESNO

题目大意：有p门的课，每门课都有若干学生，现在要为每个课程分配一名课代表，每个学生只能担任一门课的课代表，如果每个课都能找到课代表，则输出"YES"，否则"NO"。所以作为一个二分图， 只要找到最大满足数是否等于p门课就行

PS：有p门课，n个同学；之后每门课有一个m代表这门课有m个人选修，问是否满足每门课都有一个课代表；

AC代码：（没有初始化数组，导致TLE了三次）

#include <iostream>#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std ;int map[500][500] , vis[500] , link[500];int p , n ;int find(int x){for(int i = 1 ; i <=n ; i++){if(!vis[i]&&map[x][i]==1){vis[i] = 1 ;if(!link[i]||find(link[i])){link[i] = x ;return 1 ;}}}return 0 ; }int main(){int t ;cin>>t;while(t--){memset(map,0,sizeof(map));memset(vis,0,sizeof(vis));memset(link,0,sizeof(link));int m ;scanf("%d%d",&p,&n);for(int i = 1 ; i<=p ; i++){scanf("%d",&m);while(m--){int x ;scanf("%d",&x);map[i][x] = 1 ;}} int sum = 0 ; for(int i = 1 ; i <= p ; i++){memset(vis,0,sizeof(vis));if(find(i)) sum++;}if(sum==p) printf("YES\n");else printf("NO\n");}return 0 ;}