input: Write a function named PascalTriangle that takes an integer n as input and prints a Pascal's triangle with n rows. If n is less than or equal to 0, the function should print nothing.
  assert PascalTriangle(5) == None
  assert PascalTriangle(0) == None
  assert PascalTriangle(-1) == None
  assert PascalTriangle(3) == None
  assert PascalTriangle(1) == None
output: def PascalTriangle(n):
      if n <= 0:
          return
      for i in range(n):
          row = [1] * (i + 1)
          for j in range(1, i):
              row[j] = prev_row[j - 1] + prev_row[j]
          prev_row = row
          print(' '.join(map(str, row)))