結果

問題 No.2616 中央番目の中央値
ユーザー nono00
提出日時 2024-01-27 07:42:53
言語 C++23
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 62 ms / 2,000 ms
コード長 4,536 bytes
コンパイル時間 3,418 ms
コンパイル使用メモリ 250,312 KB
実行使用メモリ 10,328 KB
最終ジャッジ日時 2024-09-28 09:34:48
合計ジャッジ時間 5,213 ms
ジャッジサーバーID
(参考情報)
judge1 / judge5
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
other AC * 37
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 #
プレゼンテーションモードにする

#include <bits/stdc++.h>
#include <vector>
namespace nono {
template <class T>
class FenwickTree {
public:
FenwickTree(int size = 0): size_(size), data_(size_ + 1) {}
void add(int i, const T& v) {
for (++i; i <= size_; i += i & -i) {
data_[i] += v;
}
}
T sum(int i) const {
T result{};
for (; i > 0; i -= i & -i) {
result += data_[i];
}
return result;
}
T sum(int l, int r) const {
return sum(r) - sum(l);
}
private:
int size_;
std::vector<T> data_;
};
} // namespace nono
#include <iostream>
namespace nono {
namespace internal {
constexpr bool is_prime(unsigned long long n) {
for (unsigned long long i = 2; i * i <= n; i++) {
if (n % i == 0) return false;
}
return true;
}
} // namespace internal
template <unsigned long long MOD = 998244353>
class Modint {
public:
static_assert(internal::is_prime(MOD));
constexpr Modint(unsigned long long value = 0): value_(value % MOD) {}
constexpr Modint pow(long long exp) const {
Modint result(1);
Modint base(*this);
while (exp > 0) {
if (exp & 1) {
result *= base;
}
base *= base;
exp >>= 1;
}
return result;
}
constexpr Modint inv() const {
return pow(MOD - 2);
}
void set(unsigned long long value) {
if (value >= MOD) value %= MOD;
value_ = value;
}
unsigned long long get() const {
return value_;
}
friend constexpr bool operator==(const Modint lhs, const Modint rhs) {
return lhs.value_ == rhs.value_;
}
constexpr Modint& operator+=(const Modint other) {
this->value_ += other.value_;
if (this->value_ >= MOD) this->value_ -= MOD;
return *this;
}
constexpr Modint& operator-=(const Modint other) {
this->value_ += MOD - other.value_;
if (this->value_ >= MOD) this->value_ -= MOD;
return *this;
}
constexpr Modint& operator*=(const Modint other) {
this->value_ *= other.value_;
if (this->value_ >= MOD) this->value_ %= MOD;
return *this;
}
constexpr Modint& operator/=(const Modint other) {
return *this *= other.inv();
}
constexpr friend Modint operator+(const Modint lhs, const Modint rhs) {
return Modint(lhs) += rhs;
}
constexpr friend Modint operator-(const Modint lhs, const Modint rhs) {
return Modint(lhs) -= rhs;
}
constexpr friend Modint operator*(const Modint lhs, const Modint rhs) {
return Modint(lhs) *= rhs;
}
constexpr friend Modint operator/(const Modint lhs, const Modint rhs) {
return Modint(lhs) /= rhs;
}
friend std::istream& operator>>(std::istream& stream, Modint& mint) {
unsigned long long value;
stream >> value;
mint.set(value);
return stream;
}
friend std::ostream& operator<<(std::ostream& stream, Modint mint) {
stream << mint.get();
return stream;
}
private:
unsigned long long value_;
};
using Modint998244353 = Modint<998244353>;
using Modint1000000007 = Modint<1000000007>;
} // namespace nono
void solve() {
using Mint = nono::Modint998244353;
constexpr int N = 300005;
std::array<Mint, N> fact, fact_inv;
fact.fill(1);
fact_inv.fill(1);
for (int i = 1; i < N; i++) fact[i] = fact[i - 1] * i;
fact_inv[N - 1] = fact[N - 1].inv();
for (int i = N - 1; i > 0; i--) fact_inv[i - 1] = fact_inv[i] * i;
auto binom = [&](int n, int k) {
return fact.at(n) * fact_inv.at(k) * fact_inv.at(n - k);
};
int n;
std::cin >> n;
std::vector<int> p(n);
for (int i = 0; i < n; i++) std::cin >> p[i];
for (int i = 0; i < n; i++) p[i]--;
nono::FenwickTree<int> fenwick(n);
Mint ans = 0;
for (int i = 0; i < n; i++) {
int small_left = fenwick.sum(0, p[i]);
int big_left = i - small_left;
int small_right = p[i] - small_left;
int big_right = (n - p[i] - 1) - big_left;
Mint left = binom(small_left + big_right, small_left);
Mint right = binom(small_right + big_left, small_right);
ans += left * right;
fenwick.add(p[i], 1);
}
std::cout << ans << '\n';
}
int main() {
std::cin.tie(0)->sync_with_stdio(0);
std::cout << std::fixed << std::setprecision(16);
int t = 1;
while (t--) solve();
}
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