cp-templates/graph/bounded_flow.cc

struct bounded_flow {
    int n, m, S, T;
    dinic net;
    ll sum;
    vector<ll> fl;
    vector<ll> init;
    bounded_flow(int n, int m) : sum(0), n(n), m(m), S(0), T(n + 1), net(n + 1), fl(m), init(n + 1) {}
    void add_edge(int from, int to, ll low, ll high, int edge_id = -1) {
        if (edge_id != -1) {
            fl[edge_id] += low;
        }
        net.add_edge(from, to, high - low, edge_id, -1);
        init[to] += low, init[from] -= low;
    }
    void prep(int s, int t) {
        for (int i = 1; i <= n; ++i) {
            if (init[i] > 0) {
                net.add_edge(S, i, init[i], -1, -1);
                sum += init[i];
            } else if (init[i] < 0) {
                net.add_edge(i, T, -init[i], -1, -1);
            }
        }
        net.add_edge(t, s, INFLL, INF, -1);
    }
    optional<pair<ll, vector<ll>>> run_max_flow(int s, int t) {
        prep(s, t);
        if (sum != net.run(S, T)) {
            return nullopt;
        } else {
            auto res_flow = net.run(s, t);
            for (int from = 1; from <= n; ++from) {
                for (auto&& [to, cap, flow, rev, mark] : net.edges[from]) {
                    if (mark != -1 and mark != INF) {
                        fl[mark] += flow;
                    }
                }
            }
            return {{res_flow, fl}};
        }
    }
    optional<pair<ll, vector<ll>>> run_min_flow(int s, int t) {
        prep(s, t);
        if (sum != net.run(S, T)) {
            return nullopt;
        } else {
            int curr;
            for (int i = 0; i < m; ++i) {
                if (net.edges[t][i].mark == INF) {
                    net.edges[t][i].cap = 0;
                    net.edges[net.edges[t][i].to][net.edges[t][i].rev].cap = 0;
                    curr = net.edges[t][i].flow;  // WARN: real flow
                    break;
                }
            }
            curr -= net.run(t, s);
            for (int from = 1; from <= n; ++from) {
                for (auto&& [to, cap, flow, rev, mark] : net.edges[from]) {
                    if (mark != -1 and mark != INF) {
                        fl[mark] += flow;
                    }
                }
            }
            return {{curr, fl}};
        }
    }
    optional<pair<ll, vector<ll>>> run_flow(int s, int t) {  // BUG: unchecked code
        prep(s, t);
        auto res_flow = net.run(S, T);
        if (sum != res_flow) {
            return nullopt;
        } else {
            for (int from = 1; from <= n; ++from) {
                for (auto&& [to, cap, flow, rev, mark] : net.edges[from]) {
                    if (mark != -1 and mark != INF) {
                        fl[mark] += flow;
                    }
                }
            }
            return {{res_flow, fl}};
        }
    }
};