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.
解题思路：
这道题的意思是给你一个非负整数，它被拆成一个列表，如 939 变成 [9,3,9]，然后让你实现+1操作。简单方法就是从后往前判断各个数字，逢九进1。
Python实现：
class Solution:
def plusOne(self, digits):
"""
:type digits: List[int]
:rtype: List[int]
"""
if digits[-1] != 9: # 如果各位不为9，则直接加1即可
digits[-1] += 1
return digits
else:
i = len(digits) - 1
bit = 1
while i >= 0:
if digits[i] + bit == 10:
digits[i] = 0
bit = 1
else:
digits[i] += 1
bit = 0
break # 不再向前进位
i -= 1
if bit == 1: # 如果最前面仍然产生进位，则插入1，比如 99 -> 100
digits.insert(0,1)
return digits
a = [2,4,9,3,9]
b = Solution() # 24940
print(b.plusOne(a))
