Plus One
Given a non-negative number represented as an array of digits, plus one to the number.
The digits are stored such that the most significant digit is at the head of the list.
python code：
class Solution:
# @param {integer[]} digits
# @return {integer[]}
def plusOne(self, digits):
d=0
for i in range(len(digits)):
d=d*10+digits[i] #将数组组合成一个数
f=[]
d+=1
while d:
f.insert(0,d%10) #将+1之后的数拆成数组，return
d/=10
return f