zkw费用流

摘自大神：

https://blog.csdn.net/jzq233jzq/article/details/73123089

源点和汇点，每条边已知其最大流量和单位流量费用，求出其网络最大流和在最大流情况下的最小费用。
每行包含四个正整数ui、vi、wi、fi，表示第i条有向边从ui出发，到达vi，边权为wi（即该边最大流量为wi），单位流量的费用为fi。

Edmond-Karp经过修改
很像dinic
正着走spfa（SLF优化）

上代码：

int n, m, s, t;
struct edge
{
  int to, w, nx, cost;
} e[N << 1];
int fi[N];
int ce = 1;
int dis[N];
bool vis[N];
int cur[N];
int ans = 0;
inline void add(int u, int v, int w, int c)
{
  e[++ce] = edge{v, w, fi[u], c};
  fi[u] = ce;
}
int spfa()
{
  me(vis, 0);
  me(dis, 0x3f);
  deque<int> q;
  q.push_back(s);
  vis[s] = 1;
  dis[s] = 0;
  while (!q.empty())
  {
    int u = q.front();
    q.pop_front();
    for (int i = fi[u]; ~i; i = e[i].nx)
    {
      int v = e[i].to;
      if (e[i].w && dis[u] + e[i].cost < dis[v])
      {
        dis[v] = dis[u] + e[i].cost;
        if (!vis[v])
        {
          vis[v] = 1;
          if (!q.empty() && dis[v] < dis[q.front()])
            q.push_front(v);
          else
            q.push_back(v);
        }
      }
    }
    vis[u] = 0;
  }
  return dis[t] < inf;
}

int dfs(int u, int flow)
{
  if (u == t)
  {
    vis[u] = 1;
    return flow;
  }
  int used = 0;
  vis[u] = 1;
  for (int &i = cur[u]; ~i; i = e[i].nx)
  {
    int v = e[i].to;
    if ((!vis[v]||v==t) && e[i].w && dis[u] + e[i].cost == dis[v])
    {
      int di = dfs(v, min(e[i].w, flow - used));
      if (di)
        e[i].w -= di, e[i ^ 1].w += di, ans += e[i].cost * di, used += di;
      if (used == flow)
        break;
    }
  }
  return used;
}
int costflow(int s, int t)
{
  int res = 0;
  while (spfa())
  {
    vis[t] = 1;
    For(i, 1, n) cur[i] = fi[i];
    while (vis[t])
    {
      me(vis, 0);
      res += dfs(s, inf);
    }
  }
  return res;
}
int main()
{
#ifndef ONLINE_JUDGE
  file("test");
#endif
  me(fi, -1);
  sdf(n), sdf(m), sdf(s), sdf(t);
  while (m--)
  {
    int u, v, w, c;
    sdf(u), sdf(v), sdf(w), sdf(c);
    add(u, v, w, c), add(v, u, 0, -c);
  }
  int res = costflow(s, t);
  printf("%d %d", res, ans);

  return 0;
}