function findArrayQuadCombination(arr, S):
   if (arr == null OR S == null):
      return null
   n = length(arr)
   if (n < 4):
      return null
   # hashing implementation language dependent:
   pairHash = new HashTable()
   for i from 0 to n-1
      for j from i+1 to n-1
         if !pairHash.isMapped(arr[i]+arr[j]):
            pairHash.map(arr[i]+arr[j], [])
         pairHash.get(arr[i]+arr[j]).push([i, j])

   for pairSum in pairHash.getKeys()
      if pairHash.isMapped(S - pairSum):
         pairsA = pairHash.get(pairSum)
         pairsB = pairHash.get(S - pairsSum)
         combination = find4Uniques(pairsA, pairsB)
         if (combination != null):
            return combination
   return null

# Helper function.
# Gets 2 arrays of sub-arrays of 2 numbers
# Gets 4 unique numbers, from 2 sub-arrays of different arrays
function find4Uniques(A, B):
   lenA = length(A)
   lenB = length(B)
   for i from 0 to lenA-1:
      for j from 0 to lenB-1:
         if ( A[i][0] == B[j][0] OR A[i][1] == B[j][1] OR
              A[i][0] == B[j][1] OR A[i][1] == B[j][0] ):
            continue
         else:
            return [A[i][0], A[i][1], B[j][0], B[j][1]]
   return null