input: Write a function to print a staircase of height 'n', where n is an integer. If the given integer is 0 or negative, return an empty string.
  assert staircase(5)
  assert staircase(3)
  assert staircase(0)==""
  assert staircase(-1)==""
output: def staircase(n):
      if n <= 0:
          return ""
      result = ""
      for i in range(1, n + 1):
          result += " " * (n - i) + "#" * i + "\n"
      return result.strip()