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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. // Find total number of pairs (i,j), i < j,
  5. // such that abs(nums[i] + nums[j]) = target
  6.  
  7. int main()
  8. {
  9.     int n;
  10.     int target;
  11.     int res = 0;
  12.  
  13.     cin >> n >> target;
  14.  
  15.     vector<int> ar;
  16.  
  17.     for (int i = 0; i < n; i++)
  18.     {
  19.         int y;
  20.         cin >> y;
  21.         ar.push_back(y);
  22.     }
  23.  
  24.     unordered_map<int, int> mp;
  25.  
  26.     for (int j = 0; j < n; j++)
  27.     {
  28.         int def_1 =  target-ar[j];
  29.         int def_2 = -target-ar[j];
  30.  
  31.         if (mp.count(def_1))
  32.             res += mp[def_1];
  33.  
  34.         if (mp.count(def_2))
  35.             res += mp[def_2];
  36.  
  37.         mp[ar[j]]++;
  38.     }
  39.  
  40.     cout << res << endl;
  41.  
  42.     return 0;
  43. }
Success #stdin #stdout 0.01s 5308KB
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https://ideone.com/sNFm9C
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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