Submission #3791243

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;
using ll = long long;
// #define int ll
using PII = pair<ll, ll>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()

template<typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template<typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }

template<typename T> vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type
fill_v(T &t, const V &v) { t=v; }
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t, const V &v ) { for(auto &e:t) fill_v(e,v); }

template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a){
  out<<'('<<a.first<<','<<a.second<<')'; return out;
}
template<typename T>
istream& operator >> (istream& is, vector<T>& vec){
  for(T& x: vec) {is >> x;} return is;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
  out<<'['; for(T i: a) {out<<i<<',';} out<<']'; return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0}; // DRUL
const int INF = 1<<30;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;

// 二分累乗 O(funcの計算量*logE)
template<typename T=ll>
T binpow(T x, ll e, function<T(T,T)> func=[](T a, T b){return a*b%MOD;}, T d=1) {
  T ret = d, p = x;
  while(e > 0) {
    if(e%2 == 0) {p = func(p, p); e /= 2;}
    else {ret = func(ret, p); e--;}
  }
  return ret;
};

signed main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll n;
  cin >> n;
  vector<PII> a(n);
  REP(i, n) cin >> a[i].second >> a[i].first;

  sort(ALL(a), greater<>());
  vector<ll> w(n), h(n);
  REP(i, n) w[i] = a[i].second, h[i] = a[i].first;

  vector<ll> p(n), q(n);
  p[0] = h[0] * binpow(2, MOD-2);
  FOR(i, 1, n) p[i] = (p[i-1] + h[i] * binpow((i+1)*(i+2)%MOD, MOD-2)) % MOD;
  q[0] = binpow(2, MOD-2);
  FOR(i, 1, n) q[i] = (q[i-1] + binpow((i+1)*(i+2)%MOD, MOD-2)) % MOD;

  ll ans = 0;
  REP(i, n) {
    ll tmp = (p[i] - q[i] * h[i] % MOD) % MOD;
    (tmp += MOD) %= MOD;
    (ans += tmp * w[i] % MOD) % MOD;
  }
  ll fact = 1;
  REP(i, n) (fact *= i+1) %= MOD;
  (ans *= 2 * fact) %= MOD;

  cout << ans << endl;

  return 0;
}

Submission Info

Judge Result