제출 #223803

#제출 시각아이디문제언어결과실행 시간메모리
223803bortozMountains (NOI20_mountains)C++17
24 / 100
239 ms12300 KiB
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
#define fi first
#define se second

constexpr int MAXN = 1 << 19;

int fw[MAXN];

void add(int p, int v) {
  for (p++; p < MAXN; p += p & -p) {
    fw[p] += v;
  }
}

int sum(int p) {
  int r = 0;
  for (p++; p > 0; p -= p & -p) {
    r += fw[p];
  }
  return r;
}

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

  int N;
  cin >> N;
  vector<int> V(N);
  map<int, int> M;
  for (int& i : V) {
    cin >> i;
    M[i] = 0;
  }
  int x = 0;
  for (auto& p : M) {
    p.second = x++;
  }
  for (int& i : V) {
    i = M[i];
  }

  vector<int> L(N), R(N);
  for (int i = 0; i < N; i++) {
    L[i] = sum(V[i] - 1);
    add(V[i], 1);
  }
  fill(fw, fw + MAXN, 0);
  for (int i = N - 1; i >= 0; i--) {
    R[i] = sum(V[i] - 1);
    add(V[i], 1);
  }

  ll res = 0;
  for (int i = 0; i < N; i++) {
    res += 1ll * L[i] * R[i];
  }

  cout << res << endl;

  return 0;
}
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