結果

問題 No.1709 Indistinguishable by MEX
コンテスト
ユーザー keijak
提出日時 2021-10-15 22:44:01
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 225 ms / 2,000 ms
コード長 5,591 bytes
コンパイル時間 2,566 ms
コンパイル使用メモリ 206,772 KB
最終ジャッジ日時 2025-01-25 01:01:33
ジャッジサーバーID
（参考情報） 		judge5 / judge2
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 3
other AC * 26
権限があれば一括ダウンロードができます

ソースコード

diff # 

#include <bits/stdc++.h>
#define REP_(i, a_, b_, a, b, ...) \
  for (int i = (a), END_##i = (b); i < END_##i; ++i)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define ALL(x) std::begin(x), std::end(x)
using i64 = long long;
#include <atcoder/modint>
using Mint = atcoder::modint998244353;
std::ostream &operator<<(std::ostream &os, const Mint &m) {
  return os << m.val();
}

template<typename T, typename U>
inline bool chmax(T &a, U b) {
  return a < b and ((a = std::move(b)), true);
}
template<typename T, typename U>
inline bool chmin(T &a, U b) {
  return a > b and ((a = std::move(b)), true);
}
template<typename T>
inline int ssize(const T &a) {
  return (int) a.size();
}

template<class T>
inline std::ostream &print_one(const T &x, char endc) {
  if constexpr (std::is_same_v<T, bool>) {
    return std::cout << (x ? "Yes" : "No") << endc;
  } else {
    return std::cout << x << endc;
  }
}
template<class T>
inline std::ostream &print(const T &x) { return print_one(x, '\n'); }
template<typename T, typename... Ts>
std::ostream &print(const T &head, Ts... tail) {
  return print_one(head, ' '), print(tail...);
}
inline std::ostream &print() { return std::cout << '\n'; }

template<typename Container>
std::ostream &print_seq(const Container &a, std::string_view sep = " ",
                        std::string_view ends = "\n",
                        std::ostream &os = std::cout) {
  auto b = std::begin(a), e = std::end(a);
  for (auto it = std::begin(a); it != e; ++it) {
    if (it != b) os << sep;
    os << *it;
  }
  return os << ends;
}

template<typename T, typename = void>
struct is_iterable : std::false_type {};
template<typename T>
struct is_iterable<T, std::void_t<decltype(std::begin(std::declval<T>())),
                                  decltype(std::end(std::declval<T>()))>>
    : std::true_type {
};

template<typename T, typename = std::enable_if_t<
    is_iterable<T>::value && !std::is_same<T, std::string>::value>>
std::ostream &operator<<(std::ostream &os, const T &a) {
  return print_seq(a, ", ", "", (os << "{")) << "}";
}

struct VersatileInput {
  template<typename T>
  operator T() const {
    T x;
    std::cin >> x;
    return x;
  }
  struct Sized {
    std::size_t n;
    template<typename T>
    operator T() const {
      T x(n);
      for (auto &e: x) std::cin >> e;
      return x;
    }
  };
  Sized operator()(std::size_t n) const { return {n}; }
} const in;

inline void check(bool cond, const char *message = "!ERROR!") {
  if (not cond) throw std::runtime_error(message);
}

#ifdef MY_DEBUG
#include "debug_dump.hpp"
#else
#define DUMP(...)
#define cerr if(false)std::cerr
#endif

using namespace std;

// Disjoint half-open intervals [l, r) (mapping l to r).
class IntervalMap : public std::map<i64, i64> {
 private:
  // If true, automatically merges [l, c) and [c, r).
  bool merge_adjacent;

 public:
  i64 length;

  IntervalMap(bool merge_adjacent = true) : merge_adjacent(merge_adjacent), length(0) {}

  // Returns the interval [l, r) which contains p if available.
  // Otherwise returns this->end().
  std::map<i64, i64>::iterator find_interval(i64 p) {
    auto it = upper_bound(p);
    if (it != begin()) {
      --it;
      if (it->second > p) return it;
    }
    return end();
  }

  // Inserts interval [l, r)
  void add_interval(i64 l, i64 r) {
    auto itl = upper_bound(l), itr = lower_bound(r + merge_adjacent);
    if (itl != begin()) {
      --itl;
      if (itl->second <= l - merge_adjacent) ++itl;
    }
    if (itl != itr) {
      l = std::min(l, itl->first);
      r = std::max(r, std::prev(itr)->second);
      for (auto it = itl; it != itr;) {
        length -= it->second - it->first;
        it = erase(it);
      }
      //erase(itl, itr);
    }
    (*this)[l] = r;
    length += r - l;
  }

  // Are p and q in the same interval?
  bool same(i64 p, i64 q) {
    const auto it = find_interval(p);
    return it != end() and it->first <= q and q < it->second;
  }
};

template<class T = Mint>
struct Factorials {
  // factorials and inverse factorials.
  std::vector<T> fact, ifact;

  // n: max cached value.
  Factorials(int n) : fact(n + 1), ifact(n + 1) {
    assert(n >= 0);
    assert(n < T::mod());
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) {
      fact[i] = fact[i - 1] * i;
    }
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) {
      ifact[i - 1] = ifact[i] * i;
    }
  }

  // Combination (nCk)
  T C(int n, int k) const {
    if (k < 0 || k > n) return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};

auto solve() {
  int n = in;
  vector<int> P = in(n);
  vector<int> ix(n);
  REP(i, n) {
    ix[P[i]] = i;
  }
  Factorials<Mint> fs(n + 1);
  IntervalMap imap(true);
  Mint ans = 1;
  REP(i, n) {
    int j = ix[i];
    if (imap.find_interval(j) != imap.end()) continue;
    auto rit = imap.lower_bound(j);
    if (rit == imap.end() or rit == imap.begin()) {
      imap.add_interval(j, j + 1);
    } else {
      i64 r = prev(imap.end())->second;
      i64 l = imap.begin()->first;
      i64 s = (r - l) - imap.length;
      if (s > 1) {
        ans *= s;
      }
      imap.add_interval(j, j + 1);
    }
//    DUMP(i, imap, ans);
//    vector<string> dbg(n, "_");
//    for (auto[l, r]: imap) {
//      for (i64 j = l; j < r; ++j) {
//        dbg[j] = to_string(P[j]);
//      }
//    }
//    DUMP(i, dbg);
  }
  return ans;
}

int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  cout << std::fixed << std::setprecision(18);
  const int T = 1;//in;
  REP(t, T) {
    auto ans = solve();
    print(ans);
  }
}
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