66. Plus One [python]

题目：Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.You may assume the integer do not contain any leading zero, except the number 0 itself.The digits are stored such that the most significant digit is at the head of the list.就是说一组数表示成数组形式，然后加一把她仍写成数组，如999 + 1 = 1000， [9, 9, 9]-->[1, 0, 0, 0]程序：class Solution:
def plusOne(self, digits):
"""
:type digits: List[int]
:rtype: List[int]
"""
N = len(digits)
i = N-1

while digits[i] == 9:
digits[i] = 0

if i == 0:
digits.insert(0,1)
return digits
else:
i -= 1

digits[i] += 1
return digits