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  1. #include <iostream>
  2. #include <unordered_map>
  3. #include <vector>
  4.  
  5. using namespace std;
  6.  
  7. vector<int> v;
  8. unordered_map<int, int> table;
  9. unordered_map<int, int> count;
  10. unordered_map<int, int> tmp_ans;
  11. unordered_map<int, int> times;
  12.  
  13. int main(){
  14.     int n, a, target, ans = 0;
  15.     cin >> n;
  16.     while(n--){
  17.         cin >> a;
  18.         v.push_back(a);
  19.     }
  20.     cin >> target;
  21.  
  22.     for(int i = 0; i < v.size(); i++){
  23.         if(table.find(target - v[i]) == table.end()){
  24.             table[v[i]] = i;
  25.             count[v[i]]++;
  26.         }
  27.         else{
  28.             table[v[i]] = i;
  29.             count[v[i]]++;
  30.             if(target - v[i] == v[i]){
  31.                 times[target - v[i]]++;
  32.             }
  33.             else
  34.                 tmp_ans[v[i]] += count[target - v[i]];
  35.         }
  36.     }
  37.     for(auto it : times)
  38.         ans += ((it.second + 1) * it.second) / 2;
  39.     for(auto it : tmp_ans){
  40.         ans += it.second;
  41.     }
  42.  
  43.     cout << ans << "\n";
  44.     return 0;
  45. }
  46.  
  47.  
Success #stdin #stdout 0.01s 5516KB
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https://ideone.com/80PiyR
language:
C++ (gcc 8.3)
created:
1 year ago
visibility:
public

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