input: Write a function to print a Pascal triangle with a given number of rows. The function should take an integer as input and print the triangle accordingly. If the number of rows is zero, the function should print nothing.
  assert PascalTriangle(5) is None
  assert PascalTriangle(0) is None
  assert PascalTriangle(3) is 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)).center(n * 3))