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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5. int arr[]= {2,2,5,5,3,3};
  6. int n=sizeof(arr)/sizeof(arr[0]);
  7. int pairs=0;
  8. unordered_map<int, int> mp;
  9. for(int j=0;j<n;j++){
  10. int rem=arr[j]%5;
  11. if(mp.find((5-rem)%5)!=mp.end()){
  12. pairs+=mp[(5-rem)%5];
  13. }
  14. mp[rem]++;
  15. }
  16. cout<<pairs;
  17. return 0;
  18. }
  19.  
Success #stdin #stdout 0s 5320KB
stdin
Standard input is empty
stdout
5