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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define int              long long int
  4. #define double           long double
  5. inline int power(int a, int b) {
  6.     int x = 1;
  7.     while (b) {
  8.         if (b & 1) x *= a;
  9.         a *= a;
  10.         b >>= 1;
  11.     }
  12.     return x;
  13. }
  14.  
  15.  
  16. const int M = 1000000007;
  17. const int N = 3e5+9;
  18. const int INF = 2e9+1;
  19. const int LINF = 2000000000000000001;
  20.  
  21. //_ ***************************** START Below *******************************
  22.  
  23.  
  24.  
  25. vector<int> a;
  26. void consistency(int n, int k) {
  27.  
  28. 	int ans = 0;
  29. 	unordered_map<int,int> freq;
  30. 	for(int i=0; i<n; i++){
  31. 		if(freq.count(k-a[i])){
  32. 			ans += freq[k-a[i]];
  33. 		}
  34. 		freq[a[i]]++;
  35. 	}
  36.  
  37. 	cout << ans << endl;
  38. }
  39.  
  40. void solve() {
  41.  
  42.     int n, k;
  43.     cin >> n >> k;
  44.     a.resize(n);
  45.     for(int i=0; i<n; i++) cin >> a[i];
  46.     consistency(n, k) ;
  47.  
  48. }
  49.  
  50.  
  51.  
  52.  
  53.  
  54. int32_t main() {
  55.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  56.  
  57.     int t = 1;
  58.     while (t--) {
  59.         solve();
  60.     }
  61.  
  62.     return 0;
  63. }
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/M3E2Di
language:
C++14 (gcc 8.3)
created:
10 hours ago
visibility:
public

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