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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define int long long
  4.  
  5. void solve()
  6. {
  7.     int n, k;
  8.     cin >> n >> k;
  9.     vector<int> v(n);
  10.     map<int, int> mp;
  11.     for (int i = 0; i < n; i++)
  12.     {
  13.         cin >> v[i];
  14.         mp[v[i]]++;
  15.     }
  16.     int cnt = 0;
  17.     for (int i = 0; i < n; i++)
  18.     {
  19.         int l = k - v[i];
  20.         if (mp[l] > 0)
  21.         {
  22.             cnt += mp[l];
  23.             mp[v[i]] = 0;
  24.         }
  25.     }
  26.     cout << cnt;
  27. }
  28. signed main()
  29. {
  30. #ifndef ONLINE_JUDGE
  31.     freopen("input.txt", "r", stdin);
  32.     freopen("output.txt", "w", stdout);
  33. #endif
  34.     ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  35.  
  36.     solve();
  37. }
  38.  
Success #stdin #stdout 0.01s 5316KB
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5 10
5 0 0 0 0
stdout
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1
https://ideone.com/4D8HD6
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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