Dinic+当前弧优化 O(n^2m)

链式前向星的下标要从偶数开始，head初始化为-1

const int N = 105;
struct edge { int to, next, flow; }e[N*N*2];
int cnt, head[N];
namespace MaxFlow
{
    int cur[N], depth[N];
    int dfs(int u, int flow, int T)
    {
        if (u == T) return flow;
        for (int &i = cur[u]; ~i; i = e[i].next)
        {
            int v = e[i].to;
            if (depth[v] == depth[u] + 1 && e[i].flow)
            {
                int d = dfs(v, min(flow, e[i].flow), T);
                if (d)
                {
                    e[i].flow -= d;
                    e[i ^ 1].flow += d;
                    return d;
                }
            }
        }
        return 0;
    }
    bool bfs(int S, int T)
    {
        memset(depth, 0, sizeof(depth));
        std::queue<int>q;
        depth[S] = 1;
        q.push(S);
        while (!q.empty())
        {
            int u = q.front(); q.pop();
            for (int i = head[u]; ~i; i = e[i].next)
            {
                int v = e[i].to;
                if (!depth[v] && e[i].flow)
                {
                    depth[v] = depth[u] + 1;
                    q.push(v);
                }
            }
        }
        return depth[T];
    }
    int Dinic(int S, int T)
    {
        int ans = 0;
        while (bfs(S, T))
        {
            memcpy(cur, head, sizeof(head));
            while (int d = dfs(S, 0xffffff, T))
                ans += d;
        }
        return ans;
    }
}

最小费用最大流

head初始化为0，边的编号要从偶数开始 一般取0

const int MAXN = 150;
struct Edge { int to, next, cost, flow; }e[MAXN*MAXN * 2];
int cnt, head[MAXN];
namespace MinCostFlow
{
    int dis[MAXN], pre[MAXN];
    bool vis[MAXN];
    bool SPFA(int s, int t)
    {
        std::queue<int>q;
        memset(dis, 127, sizeof(dis));
        memset(vis, false, sizeof(vis));
        memset(pre, -1, sizeof(pre));
        dis[s] = 0;
        vis[s] = true;
        q.push(s);
        while (!q.empty())
        {
            int u = q.front(); q.pop();
            vis[u] = false;
            for (int i = head[u]; i != -1; i = e[i].next)
            {
                int v = e[i].to;
                if (dis[v] > dis[u] + e[i].cost && e[i].flow > 0)
                {
                    dis[v] = dis[u] + e[i].cost;
                    pre[v] = i;
                    if (!vis[v])
                    {
                        vis[v] = true;
                        q.push(v);
                    }
                }
            }
        }
        return pre[t] != -1;
    }
    void MCMF(int s, int t, int &cost, int &flow)
    {
        cost = flow = 0;
        while (SPFA(s, t))
        {
            int Min = 1 << 30;
            for (int i = pre[t]; i != -1; i = pre[e[i ^ 1].to])
                Min = std::min(Min, e[i].flow);
            for (int i = pre[t]; i != -1; i = pre[e[i ^ 1].to])
            {
                e[i].flow -= Min;
                e[i ^ 1].flow += Min;
                cost += e[i].cost * Min;
            }
            flow += Min;
        }
    }
}