leetcode066-python 加一

Given a non-empty array of digits representing a non-negative integer, plus one to the integer.

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.

You may assume the integer does not contain any leading zero, except the number 0 itself.

Example 1:

Input: [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.

Example 2:

Input: [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.

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解题要点：

1.如果遇到9就进一位，但是写的太复杂了

class Solution:
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        if digits == [9]:
            return [1,0]
        n = len(digits)-1
        if digits[n]!=9:
            digits[n] += 1
            return digits
        else:
            while n>0 :
                digits[n] = 0
                digits[n-1] += 1
                if digits[n-1]!=10:
                    break
                n = n - 1
            if digits[0] ==10:
                digits[0] = 0
                digits.insert(0, 1)
            return digits

后来借鉴改进后，取用了一个进位量ca：

class Solution:
    def plusOne(self, digits):
        """
        :type digits: List[int]
        :rtype: List[int]
        """
        n = len(digits)-1
        digits[n] += 1
        ca = 0
        while n >= 0:
            digits[n] += ca
            if digits[n] > 9:
                ca = 1
                digits[n] = 0
            else:
                ca = 0
                break
            n = n - 1
        if ca != 0:
            digits.insert(0, 1)
        return digits