BPM/flow

//usage: Flow<int> f(n); /*make graph using f.conn...*/ f.reserflow(); f.flow(0,1); f.f[][] wil have the flow values

#define MAX 404

template<class Node, class adjType, class fromType>
bool bfs(Node a, Node b, const adjType &adj, function<bool(int, int)> rc, fromType &from) {
    static Node q[MAX]; int qh = 0, qt = 0; q[qh++] = a;
    static map<Node, int> visited; static int flag = 0;
    visited[a] = ++flag;
    while (qh > qt) {
        a = q[qt++]; if (a == b) return true;
        for (Node j : adj[a]) {
            if (rc(a, j) && visited[j] != flag) {
                visited[j] = flag; q[qh++] = j; from[j] = a;
                if (j == b) return true;
            }
        }
    }
    return false;
}

template<class T>
class Flow {
public:
    int n;
    vector<set<int>> adj;
    vector<vector<T>> c, f;

    inline void connect(int a,int b,T cap) {adj[a].insert(b);adj[b].insert(a);c[a][b]=(cap);}
    inline void disconnect(int a,int b) {adj[a].erase(b);adj[b].erase(a);c[a][b]=0;}
    inline void conn(int a, int b) { connect(a, b, 1); }
    inline T residual(int i, int j){ return (c[i][j] - f[i][j]); }

    Flow(int _n=0):n(_n),adj(n,set<int>()), c(n, vector<T>(n, (T)0)), f(n, vector<T>(n, (T)0)) {}
    void resetflow() { for (int i = 0; i < n; i++) for (auto j : adj[i]) f[i][j] = 0; }
    T flow(int src = 0, int sink = 1) {
        vector<int> from(n,0);
        const auto &cc = c, &ff = f;
        while (bfs(src, sink, adj, [=,&cc,&ff](int i, int j) mutable {return ((cc[i][j] - ff[i][j]) > 0); }, from)){
            for (int b = 1; b != 0; b = from[b]){ f[from[b]][b] += 1; f[b][from[b]] -= 1; }
        }
        T sm = 0; for (int i = 2; i < n; i++) sm += f[0][i];
        return sm;
    }
};