input: Write a python function to print a right-angle triangle pattern using asterisks.
  assert print_triangle(5) == '*
  **
  ***
  ****
  *****'
  assert print_triangle(3) == '*
  **
  ***'
  assert print_triangle(1) == '*'
output: def print_triangle(n):
      return '\n'.join('*' * i for i in range(1, n + 1))