input: Write a function to print Pascal's Triangle.
  assert printPascalTriangle(4) == "1\n11\n121\n1331"
  assert printPascalTriangle(5) == "1\n11\n121\n1331\n14641"
  assert printPascalTriangle(1) == "1"
output: def printPascalTriangle(n):
      if n <= 0:
          return ""
      result = []
      for line in range(n):
          row = [1] * (line + 1)
          for i in range(1, line):
              row[i] = result[line-1][i-1] + result[line-1][i]
          result.append(row)
      return '\n'.join(''.join(map(str, row)) for row in result)