[LeetCode] 66. Plus One_Easy tag: array

Given a non-empty array of decimal digits representing a non-negative integer, increment 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 contains a single digit.

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

 

Example 1:

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

Example 2:

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

Example 3:

Input: digits = [0]
Output: [1]

 

Constraints:

• 1 <= digits.length <= 100
• 0 <= digits[i] <= 9

Ideas

1. reverse digits

2. pre = 1

3. 每个digit + pre

4. 更新digit 及pre， if not pre: 直接return

5. after all digit, if still pre, append (1) at the end.

6. return reversed digits

Code:

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        digits = digits[::-1]
        pre, n, i = 1, len(digits), 0
        while i < n:
            curSum = digits[i] + pre
            pre, digits[i] = divmod(curSum, 10)
            if not pre:
                return digits[::-1]
            i += 1
        if pre:
            digits.append(1)
        return digits[::-1]