【模板】有源汇有上下界最小流

版权声明：转载请声明出处，谢谢配合。 https://blog.csdn.net/zxyoi_dreamer/article/details/81878561

参考题目：loj117

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老规矩，先扔一个板子。改天更新，如有不足欢迎指正。

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代码：

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define re register
#define gc getchar
#define pc putchar
#define cs const
#define st static

inline
ll getint(){
    st ll num;
    st char c;
    for(c=gc();!isdigit(c);c=gc());
    for(num=0;isdigit(c);c=gc())num=(num<<1)+(num<<3)+(c^48);
    return num;
}

inline
void outint(ll a){
    st char ch[23];
    if(a==0)return (void)pc('0');
    while(a)ch[++ch[0]]=(a-a/10*10)^48,a/=10;
    while(ch[0])pc(ch[ch[0]--]);
}

int n,m;
int ss,tt;
ll in[50010];

int last[50010],nxt[350100],to[350100],ecnt=1;
ll cap[350100];

inline
void addedge(cs int &u,cs int &v,cs ll &val){
    nxt[++ecnt]=last[u],last[u]=ecnt,to[ecnt]=v,cap[ecnt]=val;
    nxt[++ecnt]=last[v],last[v]=ecnt,to[ecnt]=u,cap[ecnt]=0;
}

int lev[50010],cur[50010];

inline
bool BFS(){
    memset(lev,-1,sizeof lev);
    for(int re i=ss;i<=tt;++i)cur[i]=last[i];
    queue<int > q;
    q.push(ss),lev[ss]=0;
    while(!q.empty()){
        int u=q.front();
        q.pop();
        for(int re e=last[u],v=to[e];e;e=nxt[e],v=to[e]){
            if(cap[e]&&lev[v]==-1){
                lev[v]=lev[u]+1;
                if(v==tt)return true;
                q.push(v);
            }
        }
    }
    return false;
}

inline
ll Dinic(cs int &u,cs ll &flow){
    if(u==tt)return flow;
    ll ans=0;
    for(int &e=cur[u],v=to[e];e;e=nxt[e],v=to[e]){
        if(cap[e]&&lev[v]>lev[u]){
            ll delta=Dinic(v,min(flow-ans,cap[e]));
            if(delta){
                cap[e]-=delta;
                cap[e^1]+=delta;
                ans+=delta;
                if(ans==flow)return ans;
            }
        }
    }
    lev[u]=-1;
    return ans;
}

inline
ll maxflow(){
    ll ans=0;
    while(BFS())ans+=Dinic(ss,(1ll<<62)-1);
    return ans;
}

int main(){
    int s,t;
    n=getint();
    m=getint();
    s=getint();
    t=getint();
    for(int re i=1;i<=m;++i){
        int u=getint(),v=getint();
        ll l=getint(),r=getint();
        in[u]+=l;in[v]-=l;
        addedge(u,v,r-l);
    }
    tt=n+1;
    ll sum=0;
    for(int re i=1;i<=n;++i){
        if(in[i]>0)sum+=in[i],addedge(i,tt,in[i]);
        if(in[i]<0)addedge(ss,i,-in[i]);
    }
    ll flow=maxflow();
    addedge(t,s,(1ll<<62)-1);
    flow+=maxflow();
    if(flow!=sum)puts("please go home to sleep");
    else outint(cap[ecnt]);
    return 0;
}