网络流-费用流模板

代码中求的是最小费用最大流，求最大费用最大流只需要在设置边权时设置为原权值的相反数，执行一次最小费用最大流，计算得出最小费用的相反数就是要求的最大费用。

u[x], v[x], w[x], c[x] 分别表示 x 号边的出发点，到达点，权值和残量。

int SPFA()
{
    int head, tail, i, node, p;
    for (i = 1; i <= ver; ++i) {
        dis[i] = INF;
        path[i] = 0;
        bok[i] = false;
    }
    dis[s] = 0;
    head = tail = 1;
    que[tail++] = s;
    bok[s] = true;
    while (head < tail) {
        node = que[head++];
        bok[node] = false;
        for (p = fst[node]; p; p = nxt[p]) {
            if (c[p] <= 0 || dis[node] + w[p] >= dis[v[p]])
                continue;
            dis[v[p]] = dis[node] + w[p];
            path[v[p]] = p;
            if (bok[v[p]])
                continue;
            que[tail++] = v[p];
            bok[v[p]] = true;
        }
    }
    return dis[t];
}
void modify()
{
    int tmp = INF;
    for (p = path[t]; p; p = path[u[p]])
        tmp = min(c[p], tmp);
    cost += tmp * dis[t];
    maxflow += tmp;
    for (p = path[t]; p; p = path[u[p]]) {
        c[p] -= tmp;
        c[p + 1] += tmp;
    }
    return ;
}

int main()
{
    /* input */
    while (SPFA() < INF)
        modify();
    /* now we get 'cost' and 'maxflow' */
    return 0;
}