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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. using ll = long long;
  5.  
  6. const int N = 2e5+5;
  7.  
  8. int n, a[N], last[N], pos[N];
  9.  
  10. int bit[N];
  11. void update(int p, int v) {
  12.     for (; p <= n; p += p & -p)
  13.         bit[p] += v;
  14. }
  15. int get(int p) {
  16.     int s = 0;
  17.     for (; p > 0; p -= p & -p)
  18.         s += bit[p];
  19.     return s;
  20. }
  21. int query(int l, int r) {
  22.     if (l > r) return 0;
  23.     return get(r) - get(l - 1);
  24. }
  25.  
  26. void solve() {
  27.     cin >> n;
  28.     for (int i = 1; i <= n; i++) cin >> a[i];
  29.     for (int i = 1; i <= n; i++) {
  30.         last[i] = pos[a[i]];
  31.         pos[a[i]] = i;
  32.     }
  33.     ll ans = 0;
  34.     for (int r = 1; r <= n; r++) {
  35.         if (last[r]) update(last[r], -1); // Xóa lần xuất hiện trước đó
  36.         update(r, 1);
  37.         ans += query(last[r] + 1, r - 1); // Đếm số vị trí thỏa mãn trong đoạn [last[r] + 1, r - 1]
  38.     }
  39.     cout << ans << '\n';
  40. }
  41.  
  42. int main() {
  43.     ios_base::sync_with_stdio(false); cin.tie(NULL);
  44.  
  45.     #define TASK "ROBOTAI"
  46.     if (fopen(TASK".INP", "r")) {
  47.         freopen(TASK".INP", "r", stdin);
  48.         freopen(TASK".OUT", "w", stdout);
  49.     }
  50.  
  51.     int tests = 1; // cin >> tests;
  52.     while (tests--) solve();
  53.  
  54.     #ifndef ONLINE_JUDGE
  55.     cerr << "\nTime elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
  56.     #endif
  57.  
  58.     return 0;
  59. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/cAjx16
language:
C++14 (gcc 8.3)
created:
17 hours ago
visibility:
public

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