input: Write a function to print a staircase of height `n`, where `n` is an integer. The staircase should be printed with spaces and `#` characters, where each step of the staircase is represented by a single `#` character. If `n` is `0`, the function should print nothing.
  assert staircase(5)==None
  assert staircase(3)==None
  assert staircase(0)==None
output: def staircase(n):
      for i in range(1, n + 1):
          print(' ' * (n - i) + '#' * i)