loj#117. 有源汇有上下界最小流

//#pragma GCC optimize(2)
//#pragma GCC optimize(3)
//#pragma GCC optimize(4)
//#pragma GCC optimize("unroll-loops")
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include<iostream>
#include<queue>
#include<cstring>

using namespace std;

const int N=50003+10,maxn=125003+10,inf=0x3f3f3f3f;

struct edge{int to,Next,c,low;}e[maxn<<2];
int cnt,head[N],dis[N],in[N],out[N],cur[N],que[N];
int n,m,s,t;
void add(int u,int v,int c,int low)
{
    out[u]+=low;in[v]+=low;
    e[cnt].to=v;e[cnt].c=c;e[cnt].low=low;e[cnt].Next=head[u];head[u]=cnt++;
    e[cnt].to=u;e[cnt].c=0;e[cnt].low=low;e[cnt].Next=head[v];head[v]=cnt++;
}
bool bfs()
{
    memset(dis,-1,sizeof dis);
    dis[s]=0;
    int Head=1,last=1;que[Head]=s;
    while(Head<=last)
    {
        int x=que[Head++];
        if(x==t)return 1;
        for(int i=head[x];~i;i=e[i].Next)
        {
            int te=e[i].to;
            if(dis[te]==-1&&e[i].c>0)
            {
                dis[te]=dis[x]+1;
                que[++last]=te;
            }
        }
    }
    return 0;
}
int dfs(int x,int mx)
{
    if(x==t )return mx;
    int flow = 0, f;
    for(int i=cur[x];~i;i=e[i].Next)
    {
        int te=e[cur[x]=i].to;
        if(e[i].c>0&&dis[te]==dis[x]+1&&(f=dfs(te,min(mx-flow,e[i].c))))
        {
            e[i].c-=f;e[i^1].c+=f;flow+=f;
            if(flow == mx) break;
        }
    }
    if(!flow) dis[x] = 0; 
    return flow;
}
int maxflow()
{
    int ans=0,f;
    while(bfs())
    {
        for(int i=0;i<=n+2;i++)cur[i]=head[i];
        while((f=dfs(s,inf)))ans+=f;
    }
    return ans;
}
void init(){cnt=0;memset(head,-1,sizeof head);}
int main()
{
//    freopen("7.in","r",stdin);
    int ss,tt;
    scanf("%d%d%d%d",&n,&m,&ss,&tt);
    init();
    for(int i=1; i<=m; i++)
    {
        int a,b,c,d;
        scanf("%d%d%d%d",&a,&b,&c,&d);
        add(a,b,d-c,c);
    }
    s=n+1,t=n+2;
    int sum=0;
    for(int i=1; i<=n; i++)
    {
        if(in[i]>out[i])sum+=in[i]-out[i],add(s,i,in[i]-out[i],0);
        else add(i,t,out[i]-in[i],0);
    }
    int flow=maxflow();
    add(tt,ss,inf,0);
    flow+=maxflow();
    if(sum!=flow)puts("please go home to sleep");
    else printf("%d
",e[cnt-1].c);
    return 0;
}
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