input: Write a function to print a staircase pattern using "#" based on the given number of steps.
  assert staircase(3) == "  #\n ##\n###\n"
  assert staircase(4) == "   #\n  ##\n ###\n####\n"
  assert staircase(5) == "    #\n   ##\n  ###\n ####\n#####\n"
output: def staircase(steps):
      result = []
      for i in range(1, steps + 1):
          result.append(' ' * (steps - i) + '#' * i)
      return '\n'.join(result) + '\n'