#include <vector>
#include <iostream>

std::vector xs{ 5, 2, 2, 7, 1, 8 };
  
int main()
{
  struct pq { int p, q; double avg() const { return static_cast<double>(p) / q; } };   

  pq min_current { xs[0] + xs[1], 2 }; 
  pq min_total   { xs[0] + xs[1], 2 };
  int end_index = 2;
  
  for (int i = 2; i < xs.size(); ++i)
  {
    pq const a { min_current.p + xs[i], min_current.q + 1 };
    pq const b { xs[i - 1] + xs[i], 2 };
    min_current = a.avg() < b.avg()? a: b;
    
    if (min_current.avg() < min_total.avg())
    {
      min_total = min_current;
      end_index = i + 1;
    }
  }
  
  int const begin_index = end_index - min_total.q;
  std::cout << "the average is " << min_total.avg() << '\n'
            << "the contiguous subarray begins at index " << begin_index << '\n'
            << "the contiguous subarray has length " << min_total.q << '\n'
            << "the subarray is { ";
  for (int i = begin_index; i < end_index - 1; ++i)
    std::cout << xs[i] << ", "; 
  std::cout << xs[end_index - 1] << " }\n";
}

#include <iostream>
#include <vector>
using namespace std;

int solution( const vector<int>& A )
{
   double minAverage = 0.5 * ( A[0] + A[1] );
   int minPos = 0;
   for ( int k : { 2, 3 } )                                          // O(1)
   {
      for ( int i = 0; i + k <= A.size(); i++ )                      // O(N)
      {
         double sum = A[i];
         for ( int j = i + 1; j < i + k; j++ ) sum += A[j];          // O(1)
         double average = sum / k;
         if ( average < minAverage )
         {
            minAverage = average;
            minPos = i;
         }
      }
   }
   return minPos;
}

int main()
{
   cout << solution( { 5, 2, 2, 7, 1, 8 } ) << '\n';   // Note: returns the POSITION of the START of the min-average sequence
}