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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;
  30.      cin>>n>>k;
  31.      int arr[n],frneg[1000001]={},frpos[1000001]={},count=0;
  32.      for(int i=0;i<n;i++)
  33.      cin>>arr[i];
  34.      for(int i=0;i<n;i++)
  35.      {
  36.          if(arr[i]<0)
  37.          frneg[-arr[i]]++;
  38.          else 
  39.          frpos[arr[i]]++;
  40.      }
  41.      for(int i=0;i<n;i++)
  42.      {
  43.        if(arr[i]<0)
  44.        {
  45.           if(frneg[-arr[i]]) 
  46.           {
  47.               if(frpos[k-arr[i]])
  48.               count+=frpos[k-arr[i]];
  49.               else
  50.               count+=frneg[abs(k-arr[i])];
  51.               frneg[-arr[i]]--;
  52.           }
  53.        }
  54.        else
  55.        {
  56.          if(frpos[arr[i]]) 
  57.           {
  58.               if(frpos[k-arr[i]])
  59.               count+=frpos[k-arr[i]];
  60.               else
  61.               count+=frneg[abs(k-arr[i])];
  62.               frpos[arr[i]]--;
  63.           }  
  64.        }
  65.      }
  66.      cout<<count<<el;
  67.  
  68.     }
  69.  
  70.     return 0;
  71. }
Success #stdin #stdout 0.01s 11212KB
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https://ideone.com/70o1yv
language:
C++ (gcc 8.3)
created:
5 days ago
visibility:
public

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