There is an active exchange bounds maximum flow

Template title

Set \ (st, ed \) is given by the point sources and sinks, \ (S, T \) is a virtual point sources and sinks.

First, first into the passive exchange feasible flow:
from \ (ED \) to \ (ST \) is connected a capacity \ (INF \) side, so that in terms of \ (ST \) to \ (ED \) how much flow , can flow back, guaranteed circulation flow.

Now we find a feasible flow, the traffic flow is feasible \ (ed-> st \) anti-side traffic.

We then \ (ed-> st \) this edge removed, deleting virtual sources and sinks, seeking again from \ (st \) to \ (ed \) maximum flow, the flow is possible answers before adding.

code:

#include<bits/stdc++.h>
using namespace std;
const int maxn=210;
const int maxm=10010;
const int inf=1e9;
int n,m,cnt_edge=1,st,ed,S,T,sum,ans;
int head[maxn],cur[maxn],dep[maxn],in[maxn],out[maxn];
struct Edge{int u,v,down,up;}E[maxm];
struct edge{int to,nxt,flow;}e[(maxn+maxm)<<1];
inline int read()
{
    char c=getchar();int res=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
    while(c>='0'&&c<='9')res=res*10+c-'0',c=getchar();
    return res*f;
}
inline void add(int u,int v,int w)
{
    e[++cnt_edge].nxt=head[u];
    head[u]=cnt_edge;
    e[cnt_edge].to=v;
    e[cnt_edge].flow=w;
}
inline void addflow(int u,int v,int w){add(u,v,w);add(v,u,0);}
inline bool bfs()
{
    memset(dep,0,sizeof(dep));
    for(int i=0;i<=n+1;i++)cur[i]=head[i];
    queue<int>q;
    q.push(S);dep[S]=1;
    while(!q.empty())
    {
        int x=q.front();q.pop();
        for(int i=head[x];i;i=e[i].nxt)
        {
            int y=e[i].to;
            if(dep[y]||e[i].flow<=0)continue;
            dep[y]=dep[x]+1;q.push(y);
        }
    }
    return dep[T]>0;
}
int dfs(int x,int lim)
{
    if(x==T||lim<=0)return lim;
    int res=lim;
    for(int i=cur[x];i;i=e[i].nxt)
    {
        cur[x]=i;
        int y=e[i].to;
        if(dep[y]!=dep[x]+1||e[i].flow<=0)continue;
        int tmp=dfs(y,min(res,e[i].flow));
        if(tmp<=0)dep[y]=0;
        res-=tmp;
        e[i].flow-=tmp,e[i^1].flow+=tmp;
        if(res<=0)break;
    }
    return lim-res;
}
inline int Dinic(int x,int y)
{
    S=x,T=y;
    int res=0;
    while(bfs())res+=dfs(S,inf);
    return res;
}
int main()
{
    n=read(),m=read(),st=read(),ed=read();
    S=0,T=n+1;
    for(int i=1;i<=m;i++)E[i].u=read(),E[i].v=read(),E[i].down=read(),E[i].up=read();
    for(int i=1;i<=m;i++)addflow(E[i].u,E[i].v,E[i].up-E[i].down);
    for(int i=1;i<=m;i++)in[E[i].v]+=E[i].down,out[E[i].u]+=E[i].down;
    for(int i=1;i<=n;i++)
    {
        if(in[i]>=out[i])addflow(S,i,in[i]-out[i]),sum+=in[i]-out[i];
        else addflow(i,T,out[i]-in[i]);
    }
    add(ed,st,inf);
    if(Dinic(0,n+1)!=sum){puts("please go home to sleep");return 0;}
    ans+=e[cnt_edge^1].flow;e[cnt_edge].flow=e[cnt_edge^1].flow=0;
    for(int i=head[0];i;i=e[i].nxt)e[i].flow=e[i^1].flow=0;
    for(int i=head[n+1];i;i=e[i].nxt)e[i].flow=e[i^1].flow=0;
    ans+=Dinic(st,ed);
    printf("%d",ans);
    return 0;
}