input: Write a python function to find unique combinations of three numbers that sum up to a given targetSum.
  assert findUniqueCombos(5) == [[5, 0, 0], [4, 1, 0], [3, 2, 0], [3, 1, 1], [2, 2, 1]]
  assert findUniqueCombos(3) == [[3, 0, 0], [2, 1, 0], [1, 1, 1]]
  assert findUniqueCombos(0) == [[0, 0, 0]]
output: def findUniqueCombos(targetSum):
      result = []
      for i in range(targetSum + 1):
          for j in range(targetSum + 1 - i):
              k = targetSum - i - j
              if k >= j:
                  result.append([i, j, k])
      return result