input: Write a function to generate and print a Pascal triangle for the given number of rows. The function should take the number of rows as an argument and print the Pascal triangle in a formatted manner.
  assert PascalTriangle(5)==None 
  assert PascalTriangle(3)==None
  assert PascalTriangle(0)==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))