algorithm

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:heavy_check_mark: test/yosupo/bipartitematching.test.cpp

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Code

#define PROBLEM "https://judge.yosupo.jp/problem/bipartitematching"
#pragma region satashun
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;

template <class T>
V<T> make_vec(size_t a) {
    return V<T>(a);
}

template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return V<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())

constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }

template <class T, class U>
void chmin(T& t, const U& u) {
    if (t > u) t = u;
}
template <class T, class U>
void chmax(T& t, const U& u) {
    if (t < u) t = u;
}

template <class T>
void mkuni(vector<T>& v) {
    sort(ALL(v));
    v.erase(unique(ALL(v)), end(v));
}

template <class T>
vector<int> sort_by(const vector<T>& v, bool increasing = true) {
    vector<int> res(v.size());
    iota(res.begin(), res.end(), 0);

    if (increasing) {
        stable_sort(res.begin(), res.end(),
                    [&](int i, int j) { return v[i] < v[j]; });
    } else {
        stable_sort(res.begin(), res.end(),
                    [&](int i, int j) { return v[i] > v[j]; });
    }
    return res;
}

template <class T, class U>
istream& operator>>(istream& is, pair<T, U>& p) {
    is >> p.first >> p.second;
    return is;
}

template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << "," << p.second << ")";
    return os;
}

template <class T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) {
        is >> x;
    }
    return is;
}

template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    rep(i, v.size()) {
        if (i) os << ",";
        os << v[i];
    }
    os << "}";
    return os;
}

#ifdef LOCAL
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << H;
    debug_out(T...);
}
#define debug(...) \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

template <class T>
void scan(vector<T>& v, T offset = T(0)) {
    for (auto& x : v) {
        cin >> x;
        x += offset;
    }
}

// suc : 1 = newline, 2 = space
template <class T>
void print(T x, int suc = 1) {
    cout << x;
    if (suc == 1)
        cout << "\n";
    else if (suc == 2)
        cout << " ";
}

template <class T>
void print(const vector<T>& v, int suc = 1) {
    for (int i = 0; i < v.size(); ++i)
        print(v[i], i == int(v.size()) - 1 ? suc : 2);
}

template <class T>
void show(T x) {
    print(x, 1);
}

template <typename Head, typename... Tail>
void show(Head H, Tail... T) {
    print(H, 2);
    show(T...);
}

struct prepare_io {
    prepare_io() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    }
} prep_io;
#pragma endregion satashun

#define call_from_test
#include "../../cpp_src/graph/Dinic.hpp"
#undef call_from_test

int main() {
    int L, R, M;
    cin >> L >> R >> M;
    int n = L + R + 2;
    int s = n - 2, t = n - 1;
    Dinic<ll> g(n);

    rep(i, M) {
        int a, b;
        cin >> a >> b;
        g.add_edge(a, b + L, 1);
    }
    rep(i, L) g.add_edge(s, i, 1);
    rep(i, R) g.add_edge(i + L, t, 1);

    int K = g.max_flow(s, t);

    show(K);

    rep(i, L) {
        int mt = -1;
        for (auto e : g.g[i])
            if (e.to >= L && e.to < L + R && e.cap == 0) {
                mt = e.to;
            }
        if (mt != -1) {
            show(i, mt - L);
        }
    }

    return 0;
}
#line 1 "test/yosupo/bipartitematching.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/bipartitematching"
#pragma region satashun
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;

template <class T>
V<T> make_vec(size_t a) {
    return V<T>(a);
}

template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return V<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())

constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }

template <class T, class U>
void chmin(T& t, const U& u) {
    if (t > u) t = u;
}
template <class T, class U>
void chmax(T& t, const U& u) {
    if (t < u) t = u;
}

template <class T>
void mkuni(vector<T>& v) {
    sort(ALL(v));
    v.erase(unique(ALL(v)), end(v));
}

template <class T>
vector<int> sort_by(const vector<T>& v, bool increasing = true) {
    vector<int> res(v.size());
    iota(res.begin(), res.end(), 0);

    if (increasing) {
        stable_sort(res.begin(), res.end(),
                    [&](int i, int j) { return v[i] < v[j]; });
    } else {
        stable_sort(res.begin(), res.end(),
                    [&](int i, int j) { return v[i] > v[j]; });
    }
    return res;
}

template <class T, class U>
istream& operator>>(istream& is, pair<T, U>& p) {
    is >> p.first >> p.second;
    return is;
}

template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << "," << p.second << ")";
    return os;
}

template <class T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) {
        is >> x;
    }
    return is;
}

template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    rep(i, v.size()) {
        if (i) os << ",";
        os << v[i];
    }
    os << "}";
    return os;
}

#ifdef LOCAL
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << H;
    debug_out(T...);
}
#define debug(...) \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

template <class T>
void scan(vector<T>& v, T offset = T(0)) {
    for (auto& x : v) {
        cin >> x;
        x += offset;
    }
}

// suc : 1 = newline, 2 = space
template <class T>
void print(T x, int suc = 1) {
    cout << x;
    if (suc == 1)
        cout << "\n";
    else if (suc == 2)
        cout << " ";
}

template <class T>
void print(const vector<T>& v, int suc = 1) {
    for (int i = 0; i < v.size(); ++i)
        print(v[i], i == int(v.size()) - 1 ? suc : 2);
}

template <class T>
void show(T x) {
    print(x, 1);
}

template <typename Head, typename... Tail>
void show(Head H, Tail... T) {
    print(H, 2);
    show(T...);
}

struct prepare_io {
    prepare_io() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    }
} prep_io;
#pragma endregion satashun

#define call_from_test
#line 1 "cpp_src/graph/Dinic.hpp"
// O(V^2 E)
template <class F>
struct Dinic {
    static constexpr F INF = numeric_limits<F>::max();

    struct Edge {
        int to, rev;
        F cap;
        Edge(int to, F cap, int rev) : to(to), cap(cap), rev(rev){};
    };

    using E = Edge;

    VV<E> g;
    V<int> level, iter;

    Dinic() {}
    Dinic(int n) : g(n), level(n), iter(n) {}

    void add_edge(int from, int to, F cap) {
        g[from].emplace_back(to, cap, (int)g[to].size());
        g[to].emplace_back(from, 0, (int)g[from].size() - 1);
    }

    void bfs(int s) {
        fill(ALL(level), -1);
        queue<int> que;
        level[s] = 0;
        que.push(s);

        while (!que.empty()) {
            int v = que.front();
            que.pop();
            for (auto& e : g[v]) {
                if (e.cap > 0 && level[e.to] < 0) {
                    level[e.to] = level[v] + 1;
                    que.push(e.to);
                }
            }
        }
    }

    F dfs(int v, int t, F f) {
        if (v == t) return f;
        for (int& i = iter[v]; i < g[v].size(); i++) {
            auto& e = g[v][i];
            if (e.cap > 0 && level[v] < level[e.to]) {
                F d = dfs(e.to, t, min(f, e.cap));
                if (d > 0) {
                    e.cap -= d;
                    g[e.to][e.rev].cap += d;
                    return d;
                }
            }
        }
        return 0;
    }

    F max_flow(int s, int t) {
        F flow = 0;
        while (true) {
            bfs(s);
            if (level[t] < 0) return flow;
            fill(ALL(iter), 0);
            F f;
            while ((f = dfs(s, t, INF)) > 0) flow += f;
        }
    }

    // after calling max_flow
    // vector of {0, 1} (S side : 0)
    V<int> mincut(int S = 0) {
        V<int> vis(g.size());
        V<int> res(g.size(), 1);
        min_dfs(S, res, vis);
        return res;
    }

    void min_dfs(int v, V<int>& col, V<int>& vis) {
        col[v] = 0;
        vis[v] = 1;
        for (auto e : g[v]) {
            if (!vis[e.to] && e.cap > 0) {
                min_dfs(e.to, col, vis);
            }
        }
    }
};

// GCJ 2022 Round 2C
// mat[i][j] := 0,1 (whether i-j exists)
// (size of max_matching, assignment)
pair<int, V<int>> max_matching(const VV<int>& mat) {
    int L = SZ(mat);
    if (L == 0) {
        return mp(0, V<int>{});
    }

    int R = SZ(mat[0]);
    int cnt_node = L + R + 2;
    int S = cnt_node - 2, T = cnt_node - 1;
    Dinic<int> g(cnt_node);
    V<int> to(L, -1);

    rep(i, L) {
        g.add_edge(S, i, 1);
        rep(j, R) {
            if (mat[i][j]) {
                g.add_edge(i, j + L, 1);
            }
        }
    }
    rep(j, R) g.add_edge(j + L, T, 1);

    int mf = g.max_flow(S, T);
    rep(i, L) {
        for (auto e : g.g[i]) {
            if (e.to >= L && e.to < L + R && e.cap == 0) {
                to[i] = e.to - L;
            }
        }
    }
    return make_pair(mf, to);
}
#line 163 "test/yosupo/bipartitematching.test.cpp"
#undef call_from_test

int main() {
    int L, R, M;
    cin >> L >> R >> M;
    int n = L + R + 2;
    int s = n - 2, t = n - 1;
    Dinic<ll> g(n);

    rep(i, M) {
        int a, b;
        cin >> a >> b;
        g.add_edge(a, b + L, 1);
    }
    rep(i, L) g.add_edge(s, i, 1);
    rep(i, R) g.add_edge(i + L, t, 1);

    int K = g.max_flow(s, t);

    show(K);

    rep(i, L) {
        int mt = -1;
        for (auto e : g.g[i])
            if (e.to >= L && e.to < L + R && e.cap == 0) {
                mt = e.to;
            }
        if (mt != -1) {
            show(i, mt - L);
        }
    }

    return 0;
}
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