2502: 清理雪道 有源汇上下界最小流

连边下界是1，没有上界，跑最小流。

#include
#include
#include
#define N 105
#define M 50005
#define inf 1000000007
using namespace std;
int n,cnt,S,T,SS,TT;
int head[N],dis[N],q[N],cur[N],du[N];
int next[M],list[M],key[M];
inline int read()
{
    int a=0,f=1; char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1; c=getchar();}
    while (c>='0'&&c<='9') {a=a*10+c-'0'; c=getchar();}
    return a*f;
}
inline void insert(int x,int y,int z)
{
    next[++cnt]=head[x];
    head[x]=cnt;
    list[cnt]=y;
    key[cnt]=z;
}
inline bool BFS()
{
    memset(dis,-1,sizeof(dis));
    int t=0,w=1,x;
    q[1]=SS; dis[SS]=0;
    while (tx=q[++t];
        for (int i=head[x];i;i=next[i])
            if (key[i]&&dis[list[i]]==-1)
                dis[q[++w]=list[i]]=dis[x]+1;
    }
    return dis[TT]!=-1;
}
int find(int x,int flow)
{
    if (x==TT) return flow;
    int w,used=0;
    for (int i=cur[x];i;i=next[i])
        if (key[i]&&dis[list[i]]==dis[x]+1)
        {
            w=find(list[i],min(flow-used,key[i]));
            key[i]-=w; key[i^1]+=w; used+=w;
            if (key[i]) cur[x]=i;
            if (used==flow) return flow;
        }
    if (!used) dis[x]=-1;
    return used;
}
inline void dinic()
{
    int tmp=0;
    while (BFS())
    {
        for (int i=0;i<=TT;i++) cur[i]=head[i];
        tmp+=find(SS,inf);
    }
}
int main()
{
    n=read(); S=0; T=n+1; SS=T+1; TT=T+2; cnt=1;
    for (int i=1;i<=n;i++)
    {
        int sum=read(),x;
        du[i]-=sum;
        while (sum--)
        {
            x=read(); du[x]++;
            insert(i,x,inf);insert(x,i,0);
        }
        insert(S,i,inf); insert(i,S,0); 
        insert(i,T,inf); insert(T,i,0);
    }
    for (int i=1;i<=n;i++)
        if (du[i]>0) insert(SS,i,du[i]),insert(i,SS,0);
        else if (du[i]<0) insert(i,TT,-du[i]),insert(TT,i,0);
    dinic(); insert(T,S,inf); insert(S,T,0); dinic();
    printf("%d\n",key[cnt]);
    return 0;
}