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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. using ll = long long;
  5.  
  6. const int N = 1e6+5;
  7.  
  8. int n, a[N];
  9. int L[N], R[N], cnt[N];
  10.  
  11. int bit[N];
  12.  
  13. void update(int p, int v) {
  14.     for (; p <= n; p += p & -p) bit[p] += v;
  15. }
  16.  
  17. int query(int p) {
  18.     int s = 0;
  19.     for (; p > 0; p -= p & -p) s += bit[p];
  20.     return s;
  21. }
  22.  
  23. void solve() {
  24.     cin >> n;
  25.     vector<int> vals;
  26.     for (int i = 1; i <= n; i++) {
  27.         cin >> a[i];
  28.         vals.push_back(a[i]);
  29.     }
  30.     sort(vals.begin(), vals.end());
  31.     vals.erase(unique(vals.begin(), vals.end()), vals.end());
  32.     for (int i = 1; i <= n; i++) a[i] = lower_bound(vals.begin(), vals.end(), a[i]) - vals.begin() + 1;
  33.     for (int i = 1; i <= n; i++) L[i] = ++cnt[a[i]];
  34.     fill(cnt + 1, cnt + n + 1, 0);
  35.     for (int i = n; i >= 1; i--) R[i] = ++cnt[a[i]];
  36.     ll ans = 0;
  37.     for (int i = n; i >= 1; i--) {
  38.         if (L[i] > 1) ans += query(L[i] - 1);
  39.         update(R[i], 1);
  40.     }
  41.     cout << ans << '\n';
  42. }
  43.  
  44. int main() {
  45.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  46.  
  47.     int tests = 1; // cin >> tests;
  48.     while (tests--) solve();
  49.  
  50.     #ifdef LOCAL
  51.     cerr << "\nTime elapsed: " << clock() << " ms.\n";
  52.     #endif
  53.  
  54.     return 0;
  55. }
  56.  
Success #stdin #stdout 0s 5316KB
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https://ideone.com/kUmwcu
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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