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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define ll long long
  4. #define dd double
  5. #define ld long double
  6. #define pi 3.14159265359
  7. #define ull unsigned long long
  8. #define yes cout<<"YES\n"
  9. #define no cout<<"NO\n"
  10. #define el "\n"
  11. #define Arwa ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
  12. #define fix(x) cout<<fixed<<setprecision(x)
  13. ll gcd(ll a,ll b) {return b==0?a:gcd(b,a%b);}
  14. ll lcm(int a,int b) {return a/gcd(a,b)*b;}
  15. bool prime(ll n)
  16. {
  17. 	if(n==2) return true;
  18. 	if(n%2==0||n==1) return false;
  19. 	else { for(ll i=3; i*i<=n; i+=2) {if(n%i==0) return false;}}return true;
  20. }
  21. //here we go again
  22. int main()
  23. {
  24.     Arwa
  25.     int t=1;
  26.     //cin>>t;
  27.     while(t--)
  28.     {
  29.      int n,k,neg[1000001]={},pos[1000001]={};
  30.      ll c=0;
  31.      cin>>n>>k;
  32.      int arr[n];
  33.      for(int i=0;i<n;i++)
  34.      cin>>arr[i];
  35.      for(int i=0;i<n;i++)
  36.      {
  37.          if(arr[i]<0)
  38.          neg[abs(arr[i])]++;
  39.          else pos[arr[i]]++;
  40.      }
  41.      for(int i=0;i<n;i++)
  42.      {
  43.         if(neg[abs(arr[i])]&&arr[i]<0)
  44.         {
  45.            if(pos[k-arr[i]]&&k-arr[i]>=0) 
  46.            {
  47.            c+=pos[k-arr[i]];
  48.            neg[abs(arr[i])]--;
  49.            }
  50.            if(neg[k-arr[i]]&&k-arr[i]<0) 
  51.            {
  52.             c+=neg[abs(k-arr[i])];
  53.             neg[abs(arr[i])]--;
  54.            }
  55.         }
  56.         if(pos[arr[i]]&&arr[i]>=0)
  57.            {
  58.            if(pos[k-arr[i]]&&k-arr[i]>=0) 
  59.            {
  60.            c+=pos[k-arr[i]];
  61.            pos[arr[i]]--;
  62.            }
  63.            if(neg[abs(k-arr[i])]&&k-arr[i]<0) 
  64.            {
  65.             c+=neg[abs(k-arr[i])];
  66.             pos[arr[i]]--;
  67.            }
  68.            }
  69.         }
  70.      cout<<c<<el;
  71.     }
  72.     return 0;
  73. }
Success #stdin #stdout 0.01s 11344KB
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https://ideone.com/8igXYG
language:
C++ (gcc 8.3)
created:
5 days ago
visibility:
public

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