Codeforces 1520D. Same Differences Solution

 Explain:  Given   Aj - Ai = j-i

                       we get    Aj-j=Ai-i

So, we want count how many difference are same .

example:               index :1 2 3 4 5 6

                             array : 1 6 3 4 5 6

       index- array value    0 4 0 0 0 0

so the ans is how many time  count the   same value repeat.

  Solution in C++:

 ///La ilaha illellahu muhammadur rasulullah

///******Bismillahir-Rahmanir-Rahim******///

///Abul Hasnat  Tonmoy

///Department of CSE,23rd batch

///Islamic University,Bangladesh

1. #include <bits/stdc++.h>
2. using namespace std;
3. int main()
4. {
5. long long t,n,i,a;
6. cin>>t;
7. while(t--)
8. {
9. map<int,int>mp;
10. long long ans=0;
11. cin>>n;
12. for(i=1; i<=n; i++)
13. {
14. cin>>a;
15. ans+=mp[a-i]++;
16. }
17. cout<<ans<<endl;
18. }
19. }