感觉上边数不太多，加与不加差别不大。
但实际上去掉后快了很多。

求教是我的写法有问题还是当前弧在网格图下确实会比较劣？

代码如下：

class Network {
  private:
	int next[E], to[E]; ll fc[E];
	int head[V], now[V], cnt;

	int d[V];
	bool bfs(int S, int T) {
		memset(d, 0, sizeof(d));
		static int que[V];
		int l = 0, r = 0;
		d[S] = 1;
		now[S] = head[S];
		que[r++] = S;
		while (l != r) {
			int x = que[l++];
			for (int i = head[x]; i; i = next[i]) {
				if (!fc[i] || d[to[i]]) continue;
				d[to[i]] = d[x] + 1;
				now[to[i]] = head[to[i]];
				que[r++] = to[i];
				if (to[i] == T) return true;
			}
		}
		return false;
	}
	ll dfs(int x, int T, ll flow) {
		if (x == T) return flow;
		ll rest = flow;
		for (int &i = now[x]; i && rest; i = next[i]) {
			if (!fc[i] || d[to[i]] != d[x] + 1) continue;
			ll k = dfs(to[i], T, fc[i] < rest ? fc[i] : rest);
			if (!k) d[to[i]] = 0;
			rest -= k;
			fc[i] -= k;
			fc[i ^ 1] += k;
		}
		return flow - rest;
	}
  public:
	void clear() {
		memset(head, 0, sizeof(head));
		cnt = 2;
		return;
	}
	void add(int u, int v, ll w) {
		next[cnt] = head[u];
		to[cnt] = v;
		fc[cnt] = w;
		head[u] = cnt++;
		next[cnt] = head[v];
		to[cnt] = u;
		fc[cnt] = 0;
		head[v] = cnt++;
		return;
	}
	ll max_flow(int S, int T) {
		ll maxf = 0;
		while (bfs(S, T)) {
			ll flow = dfs(S, T, INF);
			if (!flow) break;
			maxf += flow;
		}
		return maxf;
	}
} G;