洛谷 P2763 试题库问题 （最大流）

建模为最大流，源点为 $0$ ，试题为 $1\sim n$，类型为 $n+1\sim n+k$，终点为 $n+k+1$，然后跑最大流算法即可。

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#define MAXN 1100
#define MAXM 20100
#define INF 0x3f3f3f3f
using namespace std;
int k,n,m,s,t,head[MAXN],cnt,res,d[MAXN],cur[MAXN];
struct Edge{
    int to,nxt,w;
}edge[MAXM];
void addedge(int u,int v,int w){
    edge[cnt].to=v;edge[cnt].w=w;edge[cnt].nxt=head[u];head[u]=cnt++;
    edge[cnt].to=u;edge[cnt].w=0;edge[cnt].nxt=head[v];head[v]=cnt++;
}
int bfs(){
    memset(d,INF,sizeof(d));
    queue<int> q;q.push(s);d[s]=0;cur[s]=head[s];
    while(!q.empty()){
        int u=q.front();q.pop();
        for(int i=head[u];i!=-1;i=edge[i].nxt){
            int v=edge[i].to,w=edge[i].w;
            if(!w)continue;
            if(d[v]==INF){
                q.push(v);cur[v]=head[v];d[v]=d[u]+1;
                if(v==t)return 1;
            }
        }
    }
    return 0;
}
int dfs(int u,int sum){
    if(u==t)return sum;
    int k,res=0;
    for(int i=cur[u];i!=-1&&sum;i=edge[i].nxt){
        cur[u]=i;int v=edge[i].to,w=edge[i].w;
        if(!w)continue;
        if(d[v]==d[u]+1){
            k=dfs(v,min(sum,w));
            if(!k)d[v]=INF;
            edge[i].w-=k;edge[i^1].w+=k;
            res+=k;sum-=k;
        }
    }
    return res;
}
bool dinic(){
    while(bfs())res+=dfs(s,INF);
    return res==m;
}
void proc(int u){
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to,w=edge[i].w;
        if(w==1&&v<=n)printf("%d ",v);
    }
}
int main(){
#ifdef WINE
    freopen("data.in","r",stdin);
#endif
    memset(head,-1,sizeof(head));
    scanf("%d%d",&k,&n);s=0,t=n+k+1;
    for(int i=1;i<=k;i++){
        int x;scanf("%d",&x);
        addedge(n+i,t,x);m+=x;
    }
    for(int i=1;i<=n;i++){
        int p;scanf("%d",&p);
        addedge(s,i,1);
        while(p--){
            int x;scanf("%d",&x);
            addedge(i,n+x,1);
        }
    }
    if(dinic()){
        for(int i=1;i<=k;i++){
            printf("%d: ",i);
            proc(n+i);
            printf("\n");
        }
    }else printf("No Solution!");
    return 0;
}