最小费用最大流

模板题

[洛谷P3381 【模板】最小费用最大流](https://www.luogu.org/pro
blem/P3381)

代码

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#define N 5005
#define M 100005
using namespace std;
int n, m, s, t, tot = -1, max_flow = 0, min_cost = 0;
int st[N], dis[N], cur[N], vis[N], pre[N], min_flow[N], q[N * 200];
struct node
{
	int to, last, val, f/*flow*/;
}w[M];
void add(int u, int v, int f, int ww)
{
	w[++tot].to = v;
	w[tot].last = st[u];
	w[tot].f = f;
	w[tot].val = ww;
	st[u] = tot;
}
bool spfa()
{
	int l = 0, r = 1;
	q[r] = s;
	memset(dis, 0x3f, sizeof dis);
	memset(min_flow, 0x3f, sizeof min_flow);
	memset(cur, -1, sizeof cur);
	memset(pre, -1, sizeof pre);
	dis[s] = 0;
	vis[s] = 1;
	while (l != r)
	{
		int u = q[++l];
		for (int i = st[u]; i != -1; i = w[i].last)
		{
			if (w[i].f > 0 && dis[w[i].to] > dis[u] + w[i].val)
			{
				dis[w[i].to] = dis[u] + w[i].val;
				pre[w[i].to] = u;
				cur[w[i].to] = i;
				min_flow[w[i].to] = min(min_flow[u], w[i].f);
				if (!vis[w[i].to])
				{
					vis[w[i].to] = 1;
					q[++r] = w[i].to;
				}
			}
		}
		vis[u] = 0;
	}
	return cur[t] != -1;
}
void dinic()
{
	while (spfa())
	{
		int flow = min_flow[t];
		max_flow += flow;
		min_cost += flow * dis[t];
		for (int i = t; i != s; i = pre[i])
			w[cur[i]].f -= flow, w[cur[i] ^ 1].f += flow;
	}
}
int main()
{
	scanf("%d%d%d%d", &n, &m, &s, &t);
	memset(st, -1, sizeof st);
	for (int i = 1; i <= m; i++)
	{
		int u, v, ww, f;
		scanf("%d%d%d%d", &u, &v, &f, &ww);
		add(u, v, f, ww);
		add(v, u, 0, -ww);
	}
	dinic();
	printf("%d %d\n", max_flow, min_cost);
	return 0;
}