Submission #223808

#	Time	Username	Problem	Language	Result	Execution time	Memory
223808		bortoz	Mountains (NOI20_mountains)	C++17	100 / 100	493 ms	31624 KiB

Mountains

#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<ll> V(N);
  map<ll, int> M;
  for (ll& i : V) {
    cin >> i;
    M[i] = 0;
  }
  int x = 0;
  for (auto& [k, v] : M) {
    v = x++;
  }
  for (ll& 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;
}

Compilation message (stderr)

Mountains.cpp: In function 'int main()':
Mountains.cpp:38:19: warning: unused variable 'k' [-Wunused-variable]
   for (auto& [k, v] : M) {
                   ^

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12