bipartite_dense.hpp

// vc<bitset> で biadj matrix を渡す
// N_1^2N_2/w.
// (5000,5000) で 300ms 程度で動く場合がある
// https://qoj.ac/problem/6308
// (10000?, 5000) 655ms
// https://codeforces.com/contest/1045/problem/A
// (10000, 20000) で 3837ms
// https://codeforces.com/contest/786/problem/E
template <typename BS>
struct BipartiteMatching_Dense {
  int N1, N2;
  vc<BS>& adj;
  vc<int> match_1, match_2;
  vc<int> que;
  vc<int> prev;
  BS vis;

  BipartiteMatching_Dense(vc<BS>& adj, int N1, int N2)
      : N1(N1), N2(N2), adj(adj), match_1(N1, -1), match_2(N2, -1) {
    if constexpr (is_same_v<BS, My_Bitset>) vis.resize(N2);
    FOR(s, N1) bfs(s);
  }

  void bfs(int s) {
    if (match_1[s] != -1) return;
    que.resize(N1), prev.resize(N1);
    int l = 0, r = 0;
    prev[s] = -1;
    vis.set();

    que[r++] = s;
    while (l < r) {
      int u = que[l++];
      BS cand = vis & adj[u];
      for (int v = cand._Find_first(); v < N2; v = cand._Find_next(v)) {
        vis[v] = 0;
        if (match_2[v] != -1) {
          que[r++] = match_2[v];
          prev[match_2[v]] = u;
          continue;
        }
        int a = u, b = v;
        while (a != -1) {
          int t = match_1[a];
          match_1[a] = b, match_2[b] = a, a = prev[a], b = t;
        }
        return;
      }
    }
    return;
  }

  vc<pair<int, int>> matching() {
    vc<pair<int, int>> res;
    FOR(v, N1) if (match_1[v] != -1) res.eb(v, match_1[v]);
    return res;
  }

  pair<vc<int>, vc<int>> vertex_cover() {
    vc<int> que(N1);
    int l = 0, r = 0;
    vis.set();
    vc<bool> done(N1);
    FOR(i, N1) {
      if (match_1[i] == -1) done[i] = 1, que[r++] = i;
    }
    while (l < r) {
      int a = que[l++];
      BS cand = adj[a] & vis;
      for (int b = cand._Find_first(); b < N2; b = cand._Find_next(b)) {
        vis[b] = 0;
        int to = match_2[b];
        assert(to != -1);
        if (!done[to]) done[to] = 1, que[r++] = to;
      }
    }
    vc<int> left, right;
    FOR(i, N1) if (!done[i]) left.eb(i);
    FOR(i, N2) if (!vis[i]) right.eb(i);
    return {left, right};
  }
};