常用模板

最大流：

int s,t;
int h[N],e[M],f[M],ne[M],idx;
int q[N],d[N],cur[N];
void add_edge_ (int a,int b,int c) {
    e[idx] = b;
    f[idx] = c;
    ne[idx] = h[a];
    h[a] = idx++;
}
void add_edge (int a,int b,int c) {
    add_edge_ (a,b,c),add_edge_ (b,a,0);
}
bool BFS () {
    int hh = 0,tt = -1;
    q[++tt] = s;
    memset (d,-1,sizeof (d));
    d[s] = 1;
    cur[s] = h[s];
    while (hh <= tt) {
        int u = q[hh++];
        for (int i = h[u];~i;i = ne[i]) {
            int v = e[i];
            if (d[v] == -1 && f[i]) {
                d[v] = d[u] + 1;
                cur[v] = h[v];
                if (v == t) return true;
                q[++tt] = v;
            }
        }
    }
    return false;
}
int max_flow (int u,int lim) {
    if (u == t) return lim;
    int flow = 0;
    for (int i = cur[u];~i && flow < lim;i = ne[i]) {
        cur[u] = i;
        int v = e[i];
        if (d[v] == d[u] + 1 && f[i]) {
            int tmp = max_flow (v,min (lim - flow,f[i]));
            if (!tmp) d[v] = -1;
            f[i] -= tmp,f[i ^ 1] += tmp,flow += tmp;
        }
    }
    return flow;
}
int dinic () {
    int ans = 0,flow;
    while (BFS ()) {
        while (flow = max_flow (s,INF)) ans += flow;
    }
    return ans;
}

最小费用最大流：

int s,t;
int h[N],e[M],ne[M],f[M],w[M],idx;
int q[N],d[N],flow[N],pre[N];
bool st[N];
void add_edge_ (int a,int b,int c,int d) {
    e[idx] = b;
    f[idx] = c;
    w[idx] = d;
    ne[idx] = h[a];
    h[a] = idx++;
}
void add_edge (int a,int b,int c,int d) {
    add_edge_ (a,b,c,d),add_edge_ (b,a,0,-d);
}
bool SPFA () {
    int hh = 0,tt = 0;
    q[tt++] = s;
    memset (d,-0x3f,sizeof (d));
    d[s] = 0;
    memset (flow,0,sizeof (flow));
    flow[s] = INF;
    while (hh != tt) {
        int u = q[hh++];
        if (hh == N) hh = 0;
        st[u] = false;
        for (int i = h[u];~i;i = ne[i]) {
            int v = e[i];
            if (f[i] && d[v] < d[u] + w[i]) {
                d[v] = d[u] + w[i];
                flow[v] = min (flow[u],f[i]);
                pre[v] = i;
                if (!st[v]) {
                    q[tt++] = v;
                    if (tt == N) tt = 0;
                    st[v] = true;
                }
            }
        }
    }
    return flow[t] > 0;
}
int EK () {
    int ans = 0;
    while (SPFA ()) {
        ans += d[t] * flow[t];
        for (int i = t;i != s;i = e[pre[i] ^ 1]) f[pre[i]] -= flow[t],f[pre[i] ^ 1] += flow[t];
    }
    return ans;
}