以下代码T了1,2,3个点，第4个点也跑得很慢。

#include<bits/stdc++.h>
#define ll long long
#define ri register int
using namespace std;
int read(){
	int res=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-') f=-f;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9'){
		res=(res<<1)+(res<<3)+ch-'0';
		ch=getchar();
	}
	return res*f;
}
const int inf=1e9,N=1e5+100;
struct s{
	int next,to,f;
}a[N<<1];
int head[N],cur[N],w[N],dis[N],num;
void add(int x,int y,int ff){
	a[++num].next=head[x];
	head[x]=num;
	a[num].to=y;
	a[num].f=ff;
}
void addedge(int x,int y,int ff){
	add(x,y,ff);
	add(y,x,0);
}
bool bfs(int s,int t){
	queue<int>q;
	memset(dis,0,sizeof(dis));
	dis[s]=1;q.push(s);
	while(!q.empty()){
		int k=q.front();q.pop();
		for(int i=head[k];i;i=a[i].next){
			if(a[i].f&&!dis[a[i].to]){
				dis[a[i].to]=dis[k]+1;
				q.push(a[i].to);
			}
		}
	}
	return dis[t];
}
int dinic(int p,int t,int flow){
	if(p==t) return flow;
	int ff=flow;
	for(int &i=cur[p];i&&ff;i=a[i].next){
		if(a[i].f&&dis[a[i].to]==dis[p]+1){
			int d=dinic(a[i].to,t,min(ff,a[i].f));
			a[i].f-=d;ff-=d;
			a[i^1].f+=d;
		}
	}
	return flow-ff;
}
int main(){
	int i,j,k,l,r,n,m,p,s,t,ans=0,sum=0;
//	freopen();
//	freopen();
	while(~scanf("%d%d",&n,&m)){
		memset(w,0,sizeof(w));
		memset(head,0,sizeof(head));
		num=1;ans=sum=0;
		for(i=1;i<=m;i++){
			k=read();
			w[n+i]+=k;w[n+m+1]-=k;
			addedge(n+i,n+m+1,inf-k);
		}
		for(i=1;i<=n;i++){
			k=read();l=read();
			addedge(0,i,l);
			for(j=1;j<=k;j++){
				p=read()+1;l=read();r=read();
				addedge(i,n+p,r-l);
				w[i]+=l;w[n+p]-=l;
			}
		}
		s=n+m+2;t=n+m+3;
		for(i=0;i<=n+m+1;i++){
			if(w[i]>0)
				addedge(i,t,w[i]),sum+=w[i];
			else if(w[i]<0)
				addedge(s,i,-w[i]);
		}
		addedge(n+m+1,0,inf);
		while(bfs(s,t)){
			for(i=0;i<=t;i++) cur[i]=head[i];
			ans+=dinic(s,t,inf);
		}
		if(ans!=sum){
			printf("-1\n\n");
			continue;
		}
		a[num].f=a[num-1].f=0;
		while(bfs(0,n+m+1)){
			for(i=0;i<=t;i++) cur[i]=head[i];
			ans+=dinic(0,n+m+1,inf);
		}
		printf("%d\n\n",ans);
	}
	return 0;
}

但是仅仅加了一句话后就跑得飞快：

int dinic(int p,int t,int flow){
	if(p==t) return flow;
	int ff=flow;
	for(int &i=cur[p];i&&ff;i=a[i].next){
		if(a[i].f&&dis[a[i].to]==dis[p]+1){
			int d=dinic(a[i].to,t,min(ff,a[i].f));
			a[i].f-=d;ff-=d;
			a[i^1].f+=d;
			if(!ff) return flow; //就是这里！！！
		}
	}
	return flow-ff;
}

尝试后发现如果这样写也会T:

int dinic(int p,int t,int flow){
	if(p==t) return flow;
	int ff=flow;
	for(int &i=cur[p];i&&ff;i=a[i].next){
	   if(!ff) return flow;
		if(a[i].f&&dis[a[i].to]==dis[p]+1){
			int d=dinic(a[i].to,t,min(ff,a[i].f));
			a[i].f-=d;ff-=d;
			a[i^1].f+=d;
		
		}
	}
	return flow-ff;
}

这是什么原因？求问