模板 有源汇上下界最小流 loj117

#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
typedef long long ll;
const int maxn = 51000,maxm = 800000;
ll inf = 1e16;
int cnt = 1,ss,tt,s,t,n,m;
int head[maxn],iter[maxn],dis[maxn],nxt[maxm],to[maxm];
ll flow[maxm],d[maxn],low[maxm];
bool inq[maxn]; 
void add(int a,int b,ll fl)
{
    nxt[++cnt] = head[a];
    to[cnt] = b;
    head[a] = cnt;
    flow[cnt] = fl;
    nxt[++cnt] = head[b];
    to[cnt] = a;
    head[b] = cnt;
    flow[cnt] = 0;
}
  
bool bfs()
{
    queue <int> que;
    memset(inq,0,sizeof(inq));
    que.push(tt);
    inq[tt] = 1;
    dis[tt] = 0;
    while (!que.empty())
    {
        int cur = que.front();
        que.pop();
        for (int i = head[cur];i;i = nxt[i])
        {
            int v = to[i];
            if (!inq[v] && flow[i ^ 1])
            {
                dis[v] = dis[cur] + 1;
                que.push(v);
                inq[v] = 1;
            }
        }
    }
    return inq[ss];
}
ll dfs(int u, ll delta)
{
    if(u == tt) return delta;
    ll ret = 0;
    for (int &i = iter[u];i;i = nxt[i]) if(dis[to[i]] + 1 == dis[u] && flow[i])
    {
        ll x = dfs(to[i], min(delta,flow[i]));
        ret += x;
        delta -= x;
        flow[i] -= x;
        flow[i ^ 1] += x; 
        if (delta == 0)
            break;   
    }
    return ret;
}
ll maxflow() 
{
    ll ret = 0;
    while (bfs())
    {
        for (int i = 1;i <= n + 2;i++)
            iter[i] = head[i];
        ll fl = 0;
        do
        {
               ll fl = dfs(ss,inf);
            ret += fl;
          } while (fl);
    }
    return ret;
}

//cnt = 1
int main()
{
    scanf("%d%d%d%d",&n,&m,&s,&t);
    ss = n + 1;
    tt = n + 2;
    int tx,ty;
    ll tl,tu;
    for (int i = 1;i <= m;i++)
    {
        scanf("%d%d%lld%lld",&tx,&ty,&tl,&tu);
        add(tx,ty,tu - tl);
        d[tx] -= tl;
        d[ty] += tl;
        low[i] = tl;
    }
    ll sum = 0;
    for (int i = 1;i <= n;i++)
        if (d[i] > 0)
        {
            sum += d[i];
            add(ss,i,d[i]);
        }else if (d[i] < 0)
            add(i,tt,-d[i]); 
    ll flow1 = maxflow();
    add(t,s,inf);
    ll flow2 = maxflow();
    if (flow1 + flow2 < sum)
    {
        printf("please go home to sleep");
        return 0;
    }
    printf("%lld
",flow[cnt]);
    return 0;
}