poj1469 COURSES二分图匹配

Posted 2022-11-23

题目链接：​​http://poj.org/problem?id=1469​​​
题意：有p门课，有n个学生，每门课有count个学生参加，现在每门课都要选一个代表出来，一个代表只能代表一门课，现在问你是否能对于每门课都选出一个代表出来
解析：其实就是问你这个二分图是否有完美匹配，即求最大匹配是否等于p

#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
#include <cstdio>
using namespace std;
const int maxn = 40005;
struct node

    int to,next;
edge[maxn];
int head[maxn],cnt;
int match[maxn],vis[maxn];
void init()

    memset(head,-1,sizeof(head));
    memset(match,0,sizeof(match));
    cnt = 0;

void addEdge(int from,int to)

    edge[cnt].to = to;
    edge[cnt].next = head[from];
    head[from] = cnt++;

bool dfs(int u)

    for(int i=head[u];i!=-1;i = edge[i].next)
    
        int v = edge[i].to;
        if(vis[v]) continue;
        vis[v] = 1;
        if(match[v]==0 || dfs(match[v]))
        
            match[v] = u;
            match[u] = v;
            return true;
        
    
    return false;

int main(void)

    int t;
    scanf("%d",&t);
    while(t--)
    
        int n,p;
        init();
        scanf("%d %d",&n,&p);
        for(int i=1;i<=n;i++)
        
            int m,x;
            scanf("%d",&m);
            for(int j=0;j<m;j++)
            
                scanf("%d",&x);
                addEdge(i,x+n);
            
        
        int ans = 0;
        for(int i=1;i<=n;i++)
        
            memset(vis,0,sizeof(vis));
            if(dfs(i))
                ans++;
        
        if(ans==n)
            puts("YES");
        else
            puts("NO");
    
    return 0;