Edmonds Karp algorithm

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c_cpp
2 years ago
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struct max_flow_graph {
    struct edge {
        int u, v, cap, flow;
    };
    int n; 
    vector<edge> el; 
    vector<vector<int>> adj;
    vector<int> dist, par;
    max_flow_graph(int n) : n(n), adj(n) {}
    void add_edge(int u, int v, int w) {
        adj[u].push_back(el.size());
        el.push_back({u, v, w, 0});
        adj[v].push_back(el.size());
        el.push_back({v, u, 0, 0}); 
    }
    int send_one_flow(int s, int e) {
        int nf = INF;
        for (int u = e; u != s; u = el[par[u]].u) {
            nf = min(nf, el[par[u]].cap - el[par[u]].flow);
        }
        for (int u = e; u != s; u = el[par[u]].u) {
            el[par[u]].flow += nf;
            el[par[u]^1].flow -= nf;
        }
        return nf;
    }
    bool bfs(int s, int e) {
        dist.assign(n, INT_MAX);
        par.assign(n, 0);
        queue<int> q;
        q.push(s); dist[s] = 0;
        while (q.size()) {
            int u = q.front(); q.pop();
            if (u == e) break;
            for (int idx : adj[u]) {
                if (el[idx].cap > el[idx].flow && dist[el[idx].v] > dist[el[idx].u] + 1) {
                    dist[el[idx].v] = dist[el[idx].u] + 1;
                    par[el[idx].v] = idx;
                    q.push(el[idx].v);
                }
            }
        }
        return dist[e] < INF;
    }
    long long edmonds_karp(int s, int e) {
        long long mf = 0;
        while (bfs(s, e)) mf += send_one_flow(s, e);
        return mf;
    }
};