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  1. #include <bits/stdc++.h>
  2.  
  3. #include <ext/pb_ds/assoc_container.hpp>
  4. #include <ext/pb_ds/tree_policy.hpp>
  5. using namespace __gnu_pbds;
  6. #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
  7.  
  8.  
  9. #define ll long long
  10.  
  11. using namespace std;
  12.  
  13. int main()
  14. {
  15. 	ios::sync_with_stdio(false);
  16. 	cin.tie(nullptr), cout.tie(nullptr);
  17.  
  18.  
  19. 	ll n,k; cin >> n >> k;
  20. 	ll sum = 0;
  21. 	vector <ll> nums(n);
  22. 	map <ll,ll> mp;
  23.  
  24. 	for (ll i=0; i<n; i++) {
  25.         cin >> nums[i];
  26.  
  27.         mp[ nums[i]%k ]++;
  28. 	}
  29.  
  30. 	for (auto i:mp) {
  31.         if (mp.count(k-i.first) && i.first!=0) {
  32.             sum += min(i.second, mp[k-i.first]);
  33.         }
  34.         else if (i.first==0) {
  35.             sum += i.second/2*2;
  36.         }
  37. 	}
  38.  
  39. 	cout << sum;
  40.  
  41. 	return 0;
  42.  
  43. }
  44.  
Success #stdin #stdout 0s 5296KB
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https://ideone.com/MetFNK
language:
C++14 (gcc 8.3)
created:
2 years ago
visibility:
public

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