#codingexercise
we are given three sorted arrays and we want  to find one element from each array such that they are closest to each other. One of the ways to do this was explained this way: We could also traverse all three arrays while keeping track of maximum and minimum difference encountered with the candidate set of three elements. We traverse by choosing one element at a time in any one array by incrementing the index of the array with the minimum value.
By advancing only the minimum element, we make sure the sweep is progressive and exhaustive.
List<int> GetClosest(List<int> A, List<int> B, List<int> C)
{
var ret = new List<int>();
int i = 0;
int j = 0;
int k = 0;
int dif f = INT_MAX;
while ( i < A.Count && j < B.Count && k < C.Count)
{
   var candidates = new List<int>() { A[i], B[j], C[k] };
   int range = Math.Abs(candidates.Min() - candidates.Max());
   if ( range < diff)
   {
       diff = range;
       ret = candidates.ToList();
   }
   if (range == 0) return ret;
   if (candidates.Min() == A[i])
   {
       i++;
   } else if (candidates.Min() == B[j])
   {
       j++;
   } else {
      k++;
   }
}
return ret;

}
We don't have to sweep for average because we could enumerate all the elements of the array to find the global average. then we can find the elements closest to it in the other two arrays.
List<int> GetAveragesFromThreeSortedArrays(List<int> A, List<int> B, List<int> C)
{
var combined = A.Union(B).Union(C).ToList();
int average = combined.Avg();
return GetClosestToGiven(A, B, C, average);
}
List<int> GetClosestToGiven(List<int> A, List<int> B, List<int>C, int value)
{
assert (A.Count > 0 && B.Count > 0 && C.Count > 0);
var ret = new List<int>();
ret.Add(GetClosest(A, value)); // using binary search
ret.Add(GetClosest(B, value));
ret.Add(GetClosest(C, value));
return ret;
}
Here we simply do a binary search on a sorted list to find the element closest to the given value. The value could lie either before or after the given value in the sorted sequence.