https://leetcode.com/problems/plus-one/#/description

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.

翻译

• 给定一个代表非负整数的列表，其中每一个值代表该位的数值。
• 对该整数+1，返回新的列表
• 比如 19=[1,9] 19+1=20=[2, 0]

分析

• 设置进位符 carry=0
• 逆序遍历列表
• 所有元素均+carry list[i] += carry
• 若list[i]+carry = 10,则list[i] = 0, carry = 1; 否则carry = 0
• 若遍历结束时，carry == 1，则需要新加入一个[1],放入列表最前面，即
• [9] ->[1, 0]

# Time O（n）
class Solution(object):
    def plusOne(self, digits):
        carry = 0
        for i in range(len(digits)-1, -1, -1):
            digits[i] += carry
            if i == len(digits) - 1:
                digits[i] += 1
            if digits[i] == 10:
                digits[i] = 0
                carry = 1 # 进位标志
            else:
                carry = 0
        if carry == 1:
            digits.insert(0, 1)
        return digits