結果

問題 No.271 next_permutation (2)
ユーザー Xiaohuba
提出日時 2025-05-24 22:00:11
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 12 ms / 2,000 ms
コード長 3,752 bytes
コンパイル時間 1,725 ms
コンパイル使用メモリ 196,020 KB
実行使用メモリ 7,844 KB
最終ジャッジ日時 2025-05-24 22:00:14
合計ジャッジ時間 2,804 ms
ジャッジサーバーID
（参考情報） 		judge3 / judge4
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ファイルパターン 結果
other AC * 21
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>

using namespace std;

// #define LOCK_GETCHAR
// #define USE_INT_128
// #undef DEBUG

#ifdef DEBUG
#include <moeebius/debug.hpp>
#else
#define debug(...) (void(0))
#define Debug(...) (void(0))
#endif

#define ENABLE_IF_INT , enable_if_t<_is_integer<T>, int> = 0
template <class T> constexpr bool _is_integer = numeric_limits<T>::is_integer;
template <> constexpr bool _is_integer<bool> = false;
template <> constexpr bool _is_integer<char> = false;
#ifdef USE_INT_128
template <> constexpr bool _is_integer<__int128> = true;
template <> constexpr bool _is_integer<__uint128_t> = true;
#endif

#if !defined(_WIN32) && !defined(__CYGWIN__) && !defined(LOCK_GETCHAR)
#define getchar getchar_unlocked
#endif

#define il inline
#define mkp make_pair
#define fi first
#define se second
#define ssz(x) (signed((x).size()))
#define beg2ed(x) (x).begin(), (x).end()
#define _loop_i_t(j, k) make_signed_t<decltype((j) - (k))>
#define For(i, j, k) for (_loop_i_t(j, k) i = (j); i <= (k); ++i)
#define ForDown(i, j, k) for (_loop_i_t(j, k) i = (j); i >= decltype(i)(k); --i)
#define eb emplace_back
#ifndef ONLINE_JUDGE
#define FileIO(filename)                                                       \
  freopen(filename ".in", "r", stdin);                                         \
  freopen(filename ".out", "w", stdout)
#else
#define FileIO(filename) void(0)
#endif

using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
using db = double;
using ldb = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#ifdef USE_INT_128
using lll = __int128_t;
using ulll = __uint128_t;
#endif

// clang-format off
constexpr il ll qpow(ll x, ull y, ll mod){ ll ans = 1; x %= mod; while (y) { if (y & 1) (ans *= x) %= mod; (x *= x) %= mod; y >>= 1; } return ans; }
template<typename T> constexpr il void cmin(T & x, const T &y){ x = min(x, y); }
template<typename T> constexpr il void cmax(T & x, const T &y){ x = max(x, y); }
template<typename T ENABLE_IF_INT> il void read(T &x){ x = 0; int f = 1; int c = getchar(); while (!isdigit(c)) { if (c == '-') f = -1; c = getchar(); } while (isdigit(c)) { x = x * 10 + (c - '0'); c = getchar(); } x *= f; }
template<typename T, typename ... Args> il void read(T &x, Args &... y){ read(x), read(y...); }
// clang-format on

// File head end

namespace {
constexpr ll MAXN = 1e5 + 5, mod = 1e9 + 7, INF = ll(1e18) + 5;
int n, a[MAXN], v[MAXN], bit[MAXN];
ll K, fac[MAXN], sfac[MAXN];
void bit_add(int p, int v) {
  for (; p <= n; p += p & -p)
    bit[p] += v;
}
int bit_qry(int p) {
  int ans = 0;
  for (; p; p -= p & -p)
    ans += bit[p];
  return ans;
}
ll calc(int st, int V, ll cnt) {
  if (cnt <= V - st)
    return (st + (st + cnt - 1)) * cnt / 2 % mod;
  ll ans = ll(st + V - 1) * (V - st) / 2 % mod;
  cnt -= V - st;
  ans += ll(0 + V - 1) * V / 2 % mod * (cnt / V % mod) % mod;
  cnt %= V;
  ans += ll(0 + cnt - 1) * cnt / 2 % mod;
  return ans % mod;
}
void Main() {
  read(n, K), K--;
  if (K == -1)
    return puts("0"), void();
  For(i, 1, n) read(a[i]);
  fac[0] = sfac[0] = 1;
  For(i, 1, n) fac[i] = fac[i - 1] * i % mod;
  For(i, 1, 19) sfac[i] = sfac[i - 1] * i;
  For(i, 20, n) sfac[i] = INF;
  ll ans = 0, dlt = 0;
  For(i, 1, n) {
    v[i] = a[i] - bit_qry(a[i]) - 1;
    bit_add(a[i], 1), ans += v[i];
  }
  ForDown(i, n, 1) {
    (ans += dlt % mod * v[i]) %= mod;
    ll pre = ans;
    ll c = K / sfac[n - i];
    (ans += calc((v[i] + 1) % (n - i + 1), n - i + 1, c) * fac[n - i]) %= mod;
    (ans += (c + v[i] + 1) % (n - i + 1) * (K % sfac[n - i] % mod)) %= mod;
    ll temp = c < n - i - v[i] ? K : (n - i - v[i]) * sfac[n - i];
    dlt += temp, K -= temp;
  }
  cout << ans << '\n';
}
} // namespace

signed main() { return Main(), 0; }
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