【模板】有源汇有上下界最大流

版权声明：转载请声明出处，谢谢配合。 https://blog.csdn.net/zxyoi_dreamer/article/details/81876912

参考题目：loj116

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有时间再更新吧，等我把网络流的模板都学一遍再说。。。

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代码：

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

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;

int last[210];
int nxt[21000],to[21000],ecnt=1;
ll cap[21000];
ll in[210];

inline
void addedge(int u,int v,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[210];
int cur[210];

inline
bool BFS(){
    memset(lev,-1,sizeof lev);
    for(int re i=0;i<=n+1;++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(lev[v]==-1&&cap[e]){
                lev[v]=lev[u]+1;
                if(v==tt)return true;
                q.push(v);
            }
        }
    }
    return false;
}

inline
ll Dinic(int u,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]){
            int delta=Dinic(v,min(cap[e],flow-ans));
            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,1<<30);
    return ans;
}

int main(){
    int s,t;
    n=getint();
    m=getint();
    s=getint();
    t=getint();
    ss=0;
    tt=n+1;
    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);
    }
    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]);
    }
    addedge(t,s,1<<30); 
    if(maxflow()==sum){
        last[ss]=0,last[tt]=0;
        ss=s;
        tt=t;
        outint(maxflow());
    }
    else puts("please go home to sleep");
    return 0;
}