1 """
2 Given a non-empty array of digits representing a non-negative integer, plus one to the integer.
3 The digits are stored such that the most significant digit is at the head of the list, and each element in the array contain a single digit.
4 You may assume the integer does not contain any leading zero, except the number 0 itself.
5 Example 1:
6 Input: [1,2,3]
7 Output: [1,2,4]
8 Explanation: The array represents the integer 123.
9 Example 2:
10 Input: [4,3,2,1]
11 Output: [4,3,2,2]
12 Explanation: The array represents the integer 4321.
13 """
14 """
15 解法一：从后向前迭代。当迭代到最高位时如果要进位
16 需要再次判断，运用了insert(a, b)函数。表示在位置a前插入b元素
17 """
18 class Solution1:
19 def plusOne(self, digits):
20 carry = 0
21 digits[len(digits)-1] += 1
22 for i in range(len(digits)-1, -1, -1):
23 if digits[i]+carry == 10:
24 digits[i] = 0
25 carry = 1
26 if i == 0:
27 digits.insert(i, 1)
28 else:
29 digits[i] += carry
30 carry = 0
31 return digits
32 """
33 解法二：递归
34 """
35 class Solution2:
36 def plusOne(self, digits):
37 if len(digits) == 1 and digits[0] == 9:
38 return [1, 0]
39 if digits[-1] != 9:
40 digits[-1] += 1
41 return digits
42 else:
43 digits[-1] = 0
44 digits[:-1] = self.plusOne(digits[:-1])
45 return digits
