Submission #216900

#	Time	Username	Problem	Language	Result	Execution time	Memory
216900		quocnguyen1012	Mountains (NOI20_mountains)	C++14	100 / 100	189 ms	14216 KiB

Mountains

#include <bits/stdc++.h>

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define eb emplace_back

using namespace std;
typedef long long ll;
typedef pair<int, int> ii;

const int maxn = 3e5 + 5;

int BIT[maxn];

void upd(int i, int v)
{
  for(; i < maxn; i += i & -i)
    BIT[i] += v;
}

int sum(int i)
{
  int res = 0;
  for(; i; i -= i & -i)
    res += BIT[i];
  return res;
}

signed main(void)
{
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  #ifdef LOCAL
    freopen("A.INP", "r", stdin);
    freopen("A.OUT", "w", stdout);
  #endif // LOCAL
  int n; cin >> n;
  vector<ll> a(n); vector<int> l(n), r(n);
  vector<ll> val;
  for(auto & x : a) cin >> x;
  val = a;
  sort(val.begin(), val.end()); val.erase(unique(val.begin(), val.end()), val.end());
  for(auto & x: a){
    x = lower_bound(val.begin(), val.end(), x) - val.begin() + 1;
  }
  for(int i = 0; i < n; ++i){
    l[i] = sum(a[i] - 1);
    upd(a[i], 1);
  }
  for(auto & x : a) upd(x, -1);
  ll res = 0;
  for(int i = n - 1; i >= 0; --i){
    res += 1ll * sum(a[i] - 1) * l[i];
    upd(a[i], 1);
  }
  cout << res;
}

• 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