class Solution:
  def findMaxSumSubArray(self,k, arr):
    # Check if arra is empty
    if not arr:
      return -1

    # Pointer to leftmost index of our window
    l = 0
    # Set max_so_far to the sum 
    max_so_far = sum(arr[:k])
    curr_sum = max_so_far

    # Start iterating from size k onwards
    for r in range(k, len(arr)):
      # Add element from right into current sum
      curr_sum += arr[r]

      # Now check if our window exceeds size k
      if (r - l) + 1 > k:
        # Subtrack leftmost element of window
        curr_sum -= arr[l]
        # Shift left
        l += 1
      
      # In either case, update max
      max_so_far = max(max_so_far, curr_sum)
    
    return max_so_far