結果

問題 No.1865 Make Cycle
ユーザー nok0
提出日時 2022-03-04 21:34:49
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 988 ms / 3,000 ms
コード長 24,338 bytes
コンパイル時間 3,067 ms
コンパイル使用メモリ 230,888 KB
最終ジャッジ日時 2025-01-28 04:55:03
ジャッジサーバーID
（参考情報） 		judge4 / judge1
このコードへのチャレンジ
（要ログイン）
ファイルパターン 結果
sample AC * 4
other AC * 20
権限があれば一括ダウンロードができます
コンパイルメッセージ
/Users/nok0/Documents/Programming/nok0/cftemp.hpp: In function ‘void scanner::scan(char*)’:
/Users/nok0/Documents/Programming/nok0/cftemp.hpp:73:33: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]

ソースコード

diff #
プレゼンテーションモードにする

#line 1 "f.cpp"
/**
 *  author: nok0
 *  created: 2022.03.04 21:31:56
**/
#line 1 "/Users/nok0/Documents/Programming/nok0/cftemp.hpp"
#include <bits/stdc++.h>
using namespace std;
#pragma region Macros
// rep macro
#define foa(v, a) for(auto &v : a)
#define REPname(a, b, c, d, e, ...) e
#define REP(...) REPname(__VA_ARGS__, REP3, REP2, REP1, REP0)(__VA_ARGS__)
#define REP0(x) for(int i = 0; i < (x); ++i)
#define REP1(i, x) for(int i = 0; i < (x); ++i)
#define REP2(i, l, r) for(int i = (l); i < (r); ++i)
#define REP3(i, l, r, c) for(int i = (l); i < (r); i += (c))
#define REPSname(a, b, c, ...) c
#define REPS(...) REPSname(__VA_ARGS__, REPS1, REPS0)(__VA_ARGS__)
#define REPS0(x) for(int i = 1; i <= (x); ++i)
#define REPS1(i, x) for(int i = 1; i <= (x); ++i)
#define RREPname(a, b, c, d, e, ...) e
#define RREP(...) RREPname(__VA_ARGS__, RREP3, RREP2, RREP1, RREP0)(__VA_ARGS__)
#define RREP0(x) for(int i = (x)-1; i >= 0; --i)
#define RREP1(i, x) for(int i = (x)-1; i >= 0; --i)
#define RREP2(i, r, l) for(int i = (r)-1; i >= (l); --i)
#define RREP3(i, r, l, c) for(int i = (r)-1; i >= (l); i -= (c))
#define RREPSname(a, b, c, ...) c
#define RREPS(...) RREPSname(__VA_ARGS__, RREPS1, RREPS0)(__VA_ARGS__)
#define RREPS0(x) for(int i = (x); i >= 1; --i)
#define RREPS1(i, x) for(int i = (x); i >= 1; --i)
// name macro
#define pb push_back
#define eb emplace_back
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define popcnt(x) __builtin_popcountll(x)
template <class T = int>
using V = std::vector<T>;
template <class T = int>
using VV = std::vector<std::vector<T>>;
template <class T>
using pqup = std::priority_queue<T, std::vector<T>, std::greater<T>>;
using ll = long long;
using ld = long double;
using int128 = __int128_t;
using pii = std::pair<int, int>;
using pll = std::pair<long long, long long>;
// input macro
template <class T, class U>
std::istream &operator>>(std::istream &is, std::pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}
template <class T>
std::istream &operator>>(std::istream &is, std::vector<T> &v) {
    for(T &i : v) is >> i;
    return is;
}
std::istream &operator>>(std::istream &is, __int128_t &a) {
    std::string s;
    is >> s;
    __int128_t ret = 0;
    for(int i = 0; i < s.length(); i++)
        if('0' <= s[i] and s[i] <= '9')
            ret = 10 * ret + s[i] - '0';
    a = ret * (s[0] == '-' ? -1 : 1);
    return is;
}
namespace scanner {
void scan(int &a) { std::cin >> a; }
void scan(long long &a) { std::cin >> a; }
void scan(std::string &a) { std::cin >> a; }
void scan(char &a) { std::cin >> a; }
void scan(char a[]) { std::scanf("%s", a); }
void scan(double &a) { std::cin >> a; }
void scan(long double &a) { std::cin >> a; }
template <class T, class U>
void scan(std::pair<T, U> &p) { std::cin >> p; }
template <class T>
void scan(std::vector<T> &a) { std::cin >> a; }
void INPUT() {}
template <class Head, class... Tail>
void INPUT(Head &head, Tail &...tail) {
    scan(head);
    INPUT(tail...);
}
}  // namespace scanner
#define VEC(type, name, size)     \
    std::vector<type> name(size); \
    scanner::INPUT(name)
#define VVEC(type, name, h, w)                                    \
    std::vector<std::vector<type>> name(h, std::vector<type>(w)); \
    scanner::INPUT(name)
#define INT(...)     \
    int __VA_ARGS__; \
    scanner::INPUT(__VA_ARGS__)
#define LL(...)            \
    long long __VA_ARGS__; \
    scanner::INPUT(__VA_ARGS__)
#define STR(...)             \
    std::string __VA_ARGS__; \
    scanner::INPUT(__VA_ARGS__)
#define CHAR(...)     \
    char __VA_ARGS__; \
    scanner::INPUT(__VA_ARGS__)
#define DOUBLE(...)     \
    double __VA_ARGS__; \
    scanner::INPUT(__VA_ARGS__)
#define LD(...)              \
    long double __VA_ARGS__; \
    scanner::INPUT(__VA_ARGS__)
// output-macro
template <class T, class U>
std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &p) {
    os << p.first << " " << p.second;
    return os;
}
template <class T>
std::ostream &operator<<(std::ostream &os, const std::vector<T> &a) {
    for(int i = 0; i < int(a.size()); ++i) {
        if(i) os << " ";
        os << a[i];
    }
    return os;
}
std::ostream &operator<<(std::ostream &dest, __int128_t &value) {
    std::ostream::sentry s(dest);
    if(s) {
        __uint128_t tmp = value < 0 ? -value : value;
        char buffer[128];
        char *d = std::end(buffer);
        do {
            --d;
            *d = "0123456789"[tmp % 10];
            tmp /= 10;
        } while(tmp != 0);
        if(value < 0) {
            --d;
            *d = '-';
        }
        int len = std::end(buffer) - d;
        if(dest.rdbuf()->sputn(d, len) != len) {
            dest.setstate(std::ios_base::badbit);
        }
    }
    return dest;
}
template <class T>
void print(const T a) { std::cout << a << '\n'; }
template <class Head, class... Tail>
void print(Head H, Tail... T) {
    std::cout << H << ' ';
    print(T...);
}
template <class T>
void printel(const T a) { std::cout << a << '\n'; }
template <class T>
void printel(const std::vector<T> &a) {
    for(const auto &v : a)
        std::cout << v << '\n';
}
template <class Head, class... Tail>
void printel(Head H, Tail... T) {
    std::cout << H << '\n';
    printel(T...);
}
void Yes(const bool b = true) { std::cout << (b ? "Yes\n" : "No\n"); }
void No() { std::cout << "No\n"; }
void YES(const bool b = true) { std::cout << (b ? "YES\n" : "NO\n"); }
void NO() { std::cout << "NO\n"; }
void err(const bool b = true) {
    if(b) {
        std::cout << "-1\n", exit(0);
    }
}
//debug macro
namespace debugger {
template <class T>
void view(const std::vector<T> &a) {
    std::cerr << "{ ";
    for(const auto &v : a) {
        std::cerr << v << ", ";
    }
    std::cerr << "\b\b }";
}
template <class T>
void view(const std::vector<std::vector<T>> &a) {
    std::cerr << "{\n";
    for(const auto &v : a) {
        std::cerr << "\t";
        view(v);
        std::cerr << "\n";
    }
    std::cerr << "}";
}
template <class T, class U>
void view(const std::vector<std::pair<T, U>> &a) {
    std::cerr << "{\n";
    for(const auto &p : a) std::cerr << "\t(" << p.first << ", " << p.second << ")\n";
    std::cerr << "}";
}
template <class T, class U>
void view(const std::map<T, U> &m) {
    std::cerr << "{\n";
    for(const auto &p : m) std::cerr << "\t[" << p.first << "] : " << p.second << "\n";
    std::cerr << "}";
}
template <class T, class U>
void view(const std::pair<T, U> &p) { std::cerr << "(" << p.first << ", " << p.second << ")"; }
template <class T>
void view(const std::set<T> &s) {
    std::cerr << "{ ";
    for(auto &v : s) {
        view(v);
        std::cerr << ", ";
    }
    std::cerr << "\b\b }";
}
template <class T>
void view(const T &e) { std::cerr << e; }
}  // namespace debugger
#ifdef LOCAL
void debug_out() {}
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    debugger::view(H);
    std::cerr << ", ";
    debug_out(T...);
}
#define debug(...)                                                \
    do {                                                          \
        std::cerr << __LINE__ << " [" << #__VA_ARGS__ << "] : ["; \
        debug_out(__VA_ARGS__);                                   \
        std::cerr << "\b\b]\n";                                   \
    } while(false)
#else
#define debug(...) (void(0))
#endif
// vector macro
template <class T>
int lb(const std::vector<T> &a, const T x) { return std::distance((a).begin(), std::lower_bound((a).begin(), (a).end(), (x))); }
template <class T>
int ub(const std::vector<T> &a, const T x) { return std::distance((a).begin(), std::upper_bound((a).begin(), (a).end(), (x))); }
template <class T>
void UNIQUE(std::vector<T> &a) {
    std::sort(a.begin(), a.end());
    a.erase(std::unique(a.begin(), a.end()), a.end());
}
template <class T>
std::vector<T> press(std::vector<T> &a) {
    auto res = a;
    UNIQUE(res);
    for(auto &v : a)
        v = lb(res, v);
    return res;
}
#define SORTname(a, b, c, ...) c
#define SORT(...) SORTname(__VA_ARGS__, SORT1, SORT0, ...)(__VA_ARGS__)
#define SORT0(a) std::sort((a).begin(), (a).end())
#define SORT1(a, c) std::sort((a).begin(), (a).end(), [](const auto x, const auto y) { return x c y; })
template <class T>
void ADD(std::vector<T> &a, const T x = 1) {
    for(auto &v : a) v += x;
}
template <class T>
void SUB(std::vector<T> &a, const T x = 1) {
    for(auto &v : a) v -= x;
}
std::vector<std::pair<char, int>> rle(const string &s) {
    int n = s.size();
    std::vector<std::pair<char, int>> ret;
    for(int l = 0; l < n;) {
        int r = l + 1;
        for(; r < n and s[l] == s[r]; r++) {}
        ret.emplace_back(s[l], r - l);
        l = r;
    }
    return ret;
}
template <class T>
std::vector<std::pair<T, int>> rle(const std::vector<T> &v) {
    int n = v.size();
    std::vector<std::pair<T, int>> ret;
    for(int l = 0; l < n;) {
        int r = l + 1;
        for(; r < n and v[l] == v[r]; r++) {}
        ret.emplace_back(v[l], r - l);
        l = r;
    }
    return ret;
}
std::vector<int> iota(int n) {
    std::vector<int> p(n);
    std::iota(p.begin(), p.end(), 0);
    return p;
}
template <class T>
struct cum_vector {
public:
    cum_vector() = default;
    template <class U>
    cum_vector(const std::vector<U> &vec) : cum((int)vec.size() + 1) {
        for(int i = 0; i < (int)vec.size(); i++)
            cum[i + 1] = cum[i] + vec[i];
    }
    T prod(int l, int r) {
        return cum[r] - cum[l];
    }
private:
    std::vector<T> cum;
};
// math macro
template <class T, class U>
inline bool chmin(T &a, const U &b) { return a > b ? a = b, true : false; }
template <class T, class U>
inline bool chmax(T &a, const U &b) { return a < b ? a = b, true : false; }
template <class T>
T divup(T x, T y) { return (x + y - 1) / y; }
template <class T>
T POW(T a, long long n) {
    T ret = 1;
    while(n) {
        if(n & 1) ret *= a;
        a *= a;
        n >>= 1;
    }
    return ret;
}
// modpow
long long POW(long long a, long long n, const int mod) {
    long long ret = 1;
    a = (a % mod + mod) % mod;
    while(n) {
        if(n & 1) (ret *= a) %= mod;
        (a *= a) %= mod;
        n >>= 1;
    }
    return ret;
}
template <class T, class F>
T bin_search(T ok, T ng, const F &f) {
    while(abs(ok - ng) > 1) {
        T mid = (ok + ng) >> 1;
        (f(mid) ? ok : ng) = mid;
    }
    return ok;
}
template <class T, class F>
T bin_search(T ok, T ng, const F &f, int loop) {
    for(int i = 0; i < loop; i++) {
        T mid = (ok + ng) / 2;
        (f(mid) ? ok : ng) = mid;
    }
    return ok;
}
// others
struct fast_io {
    fast_io() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
    }
} fast_io_;
const int inf = 1e9;
const ll INF = 1e18;
#pragma endregion
void main_();
int main() {
    main_();
    return 0;
}
#line 10 "/Users/nok0/Documents/Programming/nok0/graph/graph.hpp"
struct Edge {
    int to;
    long long cost;
    Edge() = default;
    Edge(int to_, long long cost_) : to(to_), cost(cost_) {}
    bool operator<(const Edge &a) const { return cost < a.cost; }
    bool operator>(const Edge &a) const { return cost > a.cost; }
    friend std::ostream &operator<<(std::ostream &s, Edge &a) {
        s << "to: " << a.to << ", cost: " << a.cost;
        return s;
    }
};
class graph {
    std::vector<std::vector<Edge>> edges;
    template <class F>
    struct rec_lambda {
        F f;
        rec_lambda(F &&f_) : f(std::forward<F>(f_)) {}
        template <class... Args>
        auto operator()(Args &&...args) const {
            return f(*this, std::forward<Args>(args)...);
        }
    };
public:
    inline const std::vector<Edge> &operator[](int k) const { return edges[k]; }
    inline std::vector<Edge> &operator[](int k) { return edges[k]; }
    int size() const { return edges.size(); }
    void resize(const int n) { edges.resize(n); }
    graph() = default;
    graph(int n) : edges(n) {}
    graph(int n, int e, bool weight = 0, bool directed = 0, int idx = 1) : edges(n) { input(e, weight, directed, idx); }
    const long long INF = 3e18;
    void input(int e = -1, bool weight = 0, bool directed = false, int idx = 1) {
        if(e == -1) e = size() - 1;
        while(e--) {
            int u, v;
            long long cost = 1;
            std::cin >> u >> v;
            if(weight) std::cin >> cost;
            u -= idx, v -= idx;
            edges[u].emplace_back(v, cost);
            if(!directed) edges[v].emplace_back(u, cost);
        }
    }
    void add_edge(int u, int v, long long cost = 1, bool directed = false, int idx = 0) {
        u -= idx, v -= idx;
        edges[u].emplace_back(v, cost);
        if(!directed) edges[v].emplace_back(u, cost);
    }
    // Ο(V+E)
    std::vector<long long> bfs(int s) {
        std::vector<long long> dist(size(), INF);
        std::queue<int> que;
        dist[s] = 0;
        que.push(s);
        while(!que.empty()) {
            int v = que.front();
            que.pop();
            for(auto &e : edges[v]) {
                if(dist[e.to] != INF) continue;
                dist[e.to] = dist[v] + e.cost;
                que.push(e.to);
            }
        }
        return dist;
    }
    // Ο(V+E)
    // constraint: cost of each edge is zero or one
    std::vector<long long> zero_one_bfs(int s) {
        std::vector<long long> dist(size(), INF);
        std::deque<int> deq;
        dist[s] = 0;
        deq.push_back(s);
        while(!deq.empty()) {
            int v = deq.front();
            deq.pop_front();
            for(auto &e : edges[v]) {
                assert(0LL <= e.cost and e.cost < 2LL);
                if(e.cost and dist[e.to] > dist[v] + 1) {
                    dist[e.to] = dist[v] + 1;
                    deq.push_back(e.to);
                } else if(!e.cost and dist[e.to] > dist[v]) {
                    dist[e.to] = dist[v];
                    deq.push_front(e.to);
                }
            }
        }
        return dist;
    }
    // Ο((E+V)logV)
    // cannot reach: INF
    std::vector<long long> dijkstra(int s) {  // verified
        std::vector<long long> dist(size(), INF);
        const auto compare = [](const std::pair<long long, int> &a, const std::pair<long long, int> &b) { return a.first > b.first; };
        std::priority_queue<std::pair<long long, int>, std::vector<std::pair<long long, int>>, decltype(compare)> que{compare};
        dist[s] = 0;
        que.emplace(0, s);
        while(!que.empty()) {
            std::pair<long long, int> p = que.top();
            que.pop();
            int v = p.second;
            if(dist[v] < p.first) continue;
            for(auto &e : edges[v]) {
                if(dist[e.to] > dist[v] + e.cost) {
                    dist[e.to] = dist[v] + e.cost;
                    que.emplace(dist[e.to], e.to);
                }
            }
        }
        return dist;
    }
    // Ο(VE)
    // cannot reach: INF
    // negative cycle: -INF
    std::vector<long long> bellman_ford(int s) {  // verified
        int n = size();
        std::vector<long long> res(n, INF);
        res[s] = 0;
        for(int loop = 0; loop < n - 1; loop++) {
            for(int v = 0; v < n; v++) {
                if(res[v] == INF) continue;
                for(auto &e : edges[v]) {
                    res[e.to] = std::min(res[e.to], res[v] + e.cost);
                }
            }
        }
        std::queue<int> que;
        std::vector<int> chk(n);
        for(int v = 0; v < n; v++) {
            if(res[v] == INF) continue;
            for(auto &e : edges[v]) {
                if(res[e.to] > res[v] + e.cost and !chk[e.to]) {
                    que.push(e.to);
                    chk[e.to] = 1;
                }
            }
        }
        while(!que.empty()) {
            int now = que.front();
            que.pop();
            for(auto &e : edges[now]) {
                if(!chk[e.to]) {
                    chk[e.to] = 1;
                    que.push(e.to);
                }
            }
        }
        for(int i = 0; i < n; i++)
            if(chk[i]) res[i] = -INF;
        return res;
    }
    // Ο(V^3)
    std::vector<std::vector<long long>> warshall_floyd() {  // verified
        int n = size();
        std::vector<std::vector<long long>> dist(n, std::vector<long long>(n, INF));
        for(int i = 0; i < n; i++) dist[i][i] = 0;
        for(int i = 0; i < n; i++)
            for(auto &e : edges[i]) dist[i][e.to] = std::min(dist[i][e.to], e.cost);
        for(int k = 0; k < n; k++)
            for(int i = 0; i < n; i++) {
                if(dist[i][k] == INF) continue;
                for(int j = 0; j < n; j++) {
                    if(dist[k][j] == INF) continue;
                    dist[i][j] = std::min(dist[i][j], dist[i][k] + dist[k][j]);
                }
            }
        return dist;
    }
    // Ο(V) (using DFS)
    // if a directed cycle exists, return {}
    std::vector<int> topological_sort() {  // verified
        std::vector<int> res;
        int n = size();
        std::vector<int> used(n, 0);
        bool not_DAG = false;
        for(int i = 0; i < n; i++) {
            rec_lambda([&](auto &&dfs, int k) -> void {
                if(not_DAG) return;
                if(used[k]) {
                    if(used[k] == 1) not_DAG = true;
                    return;
                }
                used[k] = 1;
                for(auto &e : edges[k]) dfs(e.to);
                used[k] = 2;
                res.push_back(k);
            })(i);
        }
        if(not_DAG) return std::vector<int>{};
        std::reverse(res.begin(), res.end());
        return res;
    }
    bool is_DAG() { return !topological_sort().empty(); }  // verified
    // Ο(V)
    // array of the distance from each vertex to the most distant vertex
    std::vector<long long> height() {  // verified
        auto vec1 = bfs(0);
        int v1 = -1, v2 = -1;
        long long dia = -1;
        for(int i = 0; i < int(size()); i++)
            if(dia < vec1[i]) dia = vec1[i], v1 = i;
        vec1 = bfs(v1);
        dia = -1;
        for(int i = 0; i < int(size()); i++)
            if(dia < vec1[i]) dia = vec1[i], v2 = i;
        auto vec2 = bfs(v2);
        for(int i = 0; i < int(size()); i++)
            if(vec1[i] < vec2[i]) vec1[i] = vec2[i];
        return vec1;
    }
    // O(V+E)
    // vector<(int)(0 or 1)>
    // if it is not bipartite, return {}
    std::vector<int> bipartite_grouping() {
        std::vector<int> colors(size(), -1);
        auto dfs = [&](auto self, int now, int col) -> bool {
            colors[now] = col;
            for(auto &e : edges[now]) {
                if(col == colors[e.to]) return false;
                if(colors[e.to] == -1 and !self(self, e.to, !col)) return false;
            }
            return true;
        };
        for(int i = 0; i < int(size()); i++)
            if(colors[i] == -1 and !dfs(dfs, i, 0)) return std::vector<int>{};
        return colors;
    }
    bool is_bipartite() { return !bipartite_grouping().empty(); }
    // Ο(V+E)
    // ((v1, v2), diameter)
    std::pair<std::pair<int, int>, long long> diameter() {  // verified
        auto vec = bfs(0);
        int v1 = -1, v2 = -1;
        long long dia = -1;
        for(int i = 0; i < int(size()); i++)
            if(dia < vec[i]) dia = vec[i], v1 = i;
        vec = bfs(v1);
        dia = -1;
        for(int i = 0; i < int(size()); i++)
            if(dia < vec[i]) dia = vec[i], v2 = i;
        std::pair<std::pair<int, int>, long long> res = {{v1, v2}, dia};
        return res;
    }
    // Ο(V+E)
    // return {s, v1, v2, ... t}
    std::vector<int> diameter_path() {
        auto vec = bfs(0);
        int v1 = -1, v2 = -1;
        long long dia = -1;
        for(int i = 0; i < int(size()); i++)
            if(dia < vec[i]) dia = vec[i], v1 = i;
        auto vec2 = bfs(v1);
        dia = -1;
        for(int i = 0; i < int(size()); i++)
            if(dia < vec2[i]) dia = vec2[i], v2 = i;
        vec = bfs(v2);
        std::vector<int> ret;
        auto dfs = [&](auto self, int now, int p) -> void {
            ret.emplace_back(now);
            if(now == v2) return;
            for(auto &[to, cost] : (*this)[now]) {
                if(vec[to] + vec2[to] == dia and to != p)
                    self(self, to, now);
            }
        };
        dfs(dfs, v1, -1);
        return ret;
    }
    // Ο(V+E)
    // return subtree_size, root = root
    std::vector<int> subtree_size(const int root) {
        int n = size();
        std::vector<int> ret(n, 1);
        rec_lambda([&](auto &&dfs, int now, int p) -> void {
            for(auto &[to, cost] : (*this)[now]) {
                if(to == p) continue;
                dfs(to, now);
                ret[now] += ret[to];
            }
        })(root, -1);
        return ret;
    }
    // Ο(ElogV)
    long long prim() {  // verified
        long long res = 0;
        std::priority_queue<Edge, std::vector<Edge>, std::greater<Edge>> que;
        for(auto &e : edges[0]) que.push(e);
        std::vector<int> chk(size());
        chk[0] = 1;
        int cnt = 1;
        while(cnt < size()) {
            auto e = que.top();
            que.pop();
            if(chk[e.to]) continue;
            cnt++;
            res += e.cost;
            chk[e.to] = 1;
            for(auto &e2 : edges[e.to]) que.push(e2);
        }
        return res;
    }
    // Ο(ElogE)
    long long kruskal() {  // verified
        std::vector<std::tuple<int, int, long long>> Edges;
        for(int i = 0; i < int(size()); i++)
            for(auto &e : edges[i]) Edges.emplace_back(i, e.to, e.cost);
        std::sort(Edges.begin(), Edges.end(), [](const std::tuple<int, int, long long> &a, const std::tuple<int, int, long long> &b) {
            return std::get<2>(a) < std::get<2>(b);
        });
        std::vector<int> uf_data(size(), -1);
        auto root = [&uf_data](auto self, int x) -> int {
            if(uf_data[x] < 0) return x;
            return uf_data[x] = self(self, uf_data[x]);
        };
        auto unite = [&uf_data, &root](int u, int v) -> bool {
            u = root(root, u), v = root(root, v);
            if(u == v) return false;
            if(uf_data[u] > uf_data[v]) std::swap(u, v);
            uf_data[u] += uf_data[v];
            uf_data[v] = u;
            return true;
        };
        long long ret = 0;
        for(auto &e : Edges)
            if(unite(std::get<0>(e), std::get<1>(e))) ret += std::get<2>(e);
        return ret;
    }
    graph build_mst() {
        std::vector<std::tuple<int, int, long long>> Edges;
        for(int i = 0; i < int(size()); i++)
            for(auto &e : edges[i]) Edges.emplace_back(i, e.to, e.cost);
        std::sort(Edges.begin(), Edges.end(), [](const std::tuple<int, int, long long> &a, const std::tuple<int, int, long long> &b) {
            return std::get<2>(a) < std::get<2>(b);
        });
        std::vector<int> uf_data(size(), -1);
        auto root = [&uf_data](auto self, int x) -> int {
            if(uf_data[x] < 0) return x;
            return uf_data[x] = self(self, uf_data[x]);
        };
        auto unite = [&uf_data, &root](int u, int v) -> bool {
            u = root(root, u), v = root(root, v);
            if(u == v) return false;
            if(uf_data[u] > uf_data[v]) std::swap(u, v);
            uf_data[u] += uf_data[v];
            uf_data[v] = u;
            return true;
        };
        graph g(this->size());
        for(auto &e : Edges)
            if(unite(std::get<0>(e), std::get<1>(e))) {
                g.add_edge(std::get<0>(e), std::get<1>(e), std::get<2>(e));
            }
        return g;
    }
    // O(V)
    std::vector<int> centroid() {
        int n = size();
        std::vector<int> centroid, sz(n);
        auto dfs = [&](auto self, int now, int per) -> void {
            sz[now] = 1;
            bool is_centroid = true;
            for(auto &e : edges[now]) {
                if(e.to != per) {
                    self(self, e.to, now);
                    sz[now] += sz[e.to];
                    if(sz[e.to] > n / 2) is_centroid = false;
                }
            }
            if(n - sz[now] > n / 2) is_centroid = false;
            if(is_centroid) centroid.push_back(now);
        };
        dfs(dfs, 0, -1);
        return centroid;
    }
    // Ο(V+E)
    // directed graph from root to leaf
    graph root_to_leaf(int root = 0) {
        graph res(size());
        std::vector<int> chk(size(), 0);
        chk[root] = 1;
        auto dfs = [&](auto self, int now) -> void {
            for(auto &e : edges[now]) {
                if(chk[e.to] == 1) continue;
                chk[e.to] = 1;
                res.add_edge(now, e.to, e.cost, 1, 0);
                self(self, e.to);
            }
        };
        dfs(dfs, root);
        return res;
    }
    // Ο(V+E)
    // directed graph from leaf to root
    graph leaf_to_root(int root = 0) {
        graph res(size());
        std::vector<int> chk(size(), 0);
        chk[root] = 1;
        auto dfs = [&](auto self, int now) -> void {
            for(auto &e : edges[now]) {
                if(chk[e.to] == 1) continue;
                chk[e.to] = 1;
                res.add_edge(e.to, now, e.cost, 1, 0);
                self(self, e.to);
            }
        };
        dfs(dfs, root);
        return res;
    }
    // long long Chu_Liu_Edmonds(int root = 0) {}
};
#line 3 "/Users/nok0/Documents/Programming/nok0/graph/scc.hpp"
struct strongly_connected_components {
private:
    enum { CHECKED = -1,
           UNCHECKED = -2 };
    const graph &graph_given;
    graph graph_reversed;
    std::vector<int> order, group_number; /* at the beginning of the building, 'group_number' is used as 'checked' */
    void dfs(int now) {
        if(group_number[now] != UNCHECKED) return;
        group_number[now] = CHECKED;
        for(auto &e : graph_given[now]) dfs(e.to);
        order.push_back(now);
    }
    void rdfs(int now, int group_count) {
        if(group_number[now] != UNCHECKED) return;
        group_number[now] = group_count;
        for(auto &e : graph_reversed[now]) rdfs(e.to, group_count);
    }
    void build(bool create_compressed_graph) {
        for(int i = 0; i < (int)graph_given.size(); i++) dfs(i);
        reverse(order.begin(), order.end());
        group_number.assign(graph_given.size(), UNCHECKED);
        int group = 0;
        for(auto &i : order)
            if(group_number[i] == UNCHECKED) rdfs(i, group), group++;
        graph_compressed.resize(group);
        groups.resize(group);
        for(int i = 0; i < (int)graph_given.size(); i++) groups[group_number[i]].push_back(i);
        if(create_compressed_graph) {
            std::vector<int> edges(group, -1);
            for(int i = 0; i < group; i++)
                for(auto &vertex : groups[i])
                    for(auto &e : graph_given[vertex])
                        if(group_number[e.to] != i and edges[group_number[e.to]] != i) {
                            edges[group_number[e.to]] = i;
                            graph_compressed[i].emplace_back(group_number[e.to], 1);
                        }
        }
        return;
    }
public:
    std::vector<std::vector<int>> groups;
    graph graph_compressed;
    strongly_connected_components(const graph &g_, bool create_compressed_graph = true)
      : graph_given(g_), graph_reversed(g_.size()), group_number(g_.size(), UNCHECKED) {
        for(size_t i = 0; i < g_.size(); i++)
            for(auto &e : graph_given[i]) graph_reversed[e.to].emplace_back(i, 1);
        build(create_compressed_graph);
    }
    const int &operator[](const int k) { return group_number[k]; }
};
#line 8 "f.cpp"
void main_() {
    INT(n, q);
    VEC(pii, ab, q);
    foa(p, ab) {
        p.first--, p.second--;
    }
    auto f = [&](int x) {
        graph g(n);
        REP(i, x) {
            auto [a, b] = ab[i];
            g.add_edge(a, b, 1, 1);
        }
        strongly_connected_components scc(g);
        return SZ(scc.graph_compressed) != n;
    };
    if(!f(q)) {
        print(-1);
        return;
    }
    print(bin_search(q, 0, f));
}
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
0