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  1. /* hng */
  2. #include <bits/stdc++.h>
  3. /*
  4. #pragma GCC optimize("O3,unroll-loops")
  5. #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
  6. */
  7. #define fast                     \
  8.     ios::sync_with_stdio(false); \
  9.     cin.tie(nullptr);            \
  10.     cout.tie(nullptr);
  11. #define fi first
  12. #define se second
  13. #define pr pair
  14. #define ll long long
  15. #define ull unsigned long long
  16. #define db double
  17. #define vt vector
  18. #define pb(a) push_back(a) //push_back()
  19. #define umap unordered_map
  20. #define ln '\n'
  21. using namespace std;
  22.  
  23. const string NAME = "test";
  24. const ll MAXN = 1e6 + 36;
  25. const ll MOD = 1e9 + 7;
  26. const ll lmin = LLONG_MIN;
  27. const ll lmax = LLONG_MAX;
  28. /*-------------------------------------------------------------*/
  29. int main()
  30. {
  31.     fast;
  32.  
  33.     #ifndef ONLINE_JUDGE
  34.     freopen((NAME + ".inp").c_str(), "r", stdin);
  35.     freopen((NAME + ".out").c_str(), "w", stdout);
  36.     #endif
  37.  
  38.     auto start = chrono::steady_clock::now();
  39.  
  40.     ll n, k;
  41.     cin >> n >> k;
  42.  
  43.     ll x;
  44.     umap<ll, ll> cnt;
  45.     ll ans = 0;
  46.  
  47.     while (n--)
  48.     {
  49.         cin >> x;
  50.         ans += cnt[x];
  51.         cnt[k - x]++;
  52.     }
  53.  
  54.     cout << ans;
  55.  
  56.     auto end = chrono::steady_clock::now();
  57.     cerr << "Time = " << chrono::duration<double>(end - start).count() << 's';
  58. }
  59.  
Success #stdin #stdout #stderr 0.01s 5288KB
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stdin
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7 12
1
5
11
4
7
3
8
stdout
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3
stderr
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Time = 2.4844e-05s
https://ideone.com/4BSDnj
language:
C++14 (gcc 8.3)
created:
2 days ago
visibility:
public

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