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  1. #include <iostream>
  2. using namespace std;
  3. #include <bits/stdc++.h>
  4. int main() {
  5. 	// your code goes here
  6. 	int  n;
  7. 	cin>>n;
  8. 	int arr[n];
  9. 	int i=0;
  10. 	while(i<n)
  11. 	 {
  12. 	 	cin>>arr[i];
  13. 	 	i++;
  14. 	 }
  15.  
  16.  
  17. 	 //int count=0;
  18. 	 unordered_map<int,int>freq;
  19.  
  20.       for(int k=2;k<=n;k++)
  21.        {
  22.        	for(int l=k+1;k<=n;k++)
  23.        	 {
  24.        	 	int sum=arr[k]+arr[l];
  25.        	 	freq[sum]++;
  26.        	 }
  27.        }
  28.  
  29.  
  30.       int count=0;
  31.  
  32. 	 for(int i=0;i<n;i++)
  33. 	  {
  34. 	  	for(int j=i+1;j<n;j++)
  35. 	  	 {
  36. 	  	 	int x = arr[i]+arr[j];
  37. 	  	 	count+=freq[-x];
  38. 	  	 }
  39. 	  }
  40. 	  cout<<count;
  41.  
  42. 	return 0;
  43. }
Success #stdin #stdout 0.01s 5288KB
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stdin
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7
1 2 3 4 -1 -2 -2
stdout
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2
https://ideone.com/QRRjDC
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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