HackerEarth The Great Kian problem solution

In this HackerEarth The Great Kian problem solution The great Kian is looking for a smart prime minister. He's looking for a guy who can solve the OLP (Old Legendary Problem). OLP is an old problem (obviously) that no one was able to solve it yet (like P=NP).

But still, you want to be the prime minister really bad. So here's the problem:

Given the sequence a1, a2, ..., an find the three values a1 + a4 + a7 + ..., a2 + a5 + a8 + ... and a3 + a6 + a9 + ... (these summations go on while the indexes are valid).

HackerEarth The Great Kian problem solution.

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define Foreach(i, c) for(__typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define For(i,a,b) for(int (i)=(a);(i) < (b); ++(i))
#define rof(i,a,b) for(int (i)=(a);(i) > (b); --(i))
#define rep(i, c) for(auto &(i) : (c))
#define x first
#define y second
#define pb push_back
#define PB pop_back()
#define iOS ios_base::sync_with_stdio(false)
#define sqr(a) (((a) * (a)))
#define all(a) a.begin() , a.end()
#define error(x) cerr << #x << " = " << (x) <<endl
#define Error(a,b) cerr<<"( "<<#a<<" , "<<#b<<" ) = ( "<<(a)<<" , "<<(b)<<" )\n";
#define errop(a) cerr<<#a<<" = ( "<<((a).x)<<" , "<<((a).y)<<" )\n";
#define coud(a,b) cout<<fixed << setprecision((b)) << (a)
#define L(x) ((x)<<1)
#define R(x) (((x)<<1)+1)
#define umap unordered_map
#define double long double
typedef long long ll;
typedef pair<int,int>pii;
typedef vector<int> vi;
typedef complex<double> point;
template <typename T> using os =  tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <class T>  inline void smax(T &x,T y){ x = max((x), (y));}
template <class T>  inline void smin(T &x,T y){ x = min((x), (y));}
ll x[3];
int main(){
  iOS;
  int n, a;
  cin >> n;
  For(i,0,n){
    cin >> a;
    x[i % 3] += (ll)a;
  }
  For(i,0,3)
    cout << x[i] << ' ';
  cout << endl;
  return 0;
}

Second solution

#include<bits/stdc++.h>

const int N = 100031;

using namespace std;

int n;
int ar[N];
long long res[10];

int main(){
  ios_base::sync_with_stdio(0);
  //cin.tie(0);

  cin >> n;

  for (int i = 0; i < n; i++)
  {
    cin >> ar[i];
  }

  for (int i = 0; i < 3; i++)
  {
    int cur = i;
    do
    {
      res[i] += ar[cur];
      cur += 3;
    } while (cur < n);
  }

  for (int i = 0; i < 3; i++)
  {
    if (i)
      cout << " ";
    cout << res[i];
  }
  cout << endl;

  return 0;
}