989. Add to Array-Form of Integer

Problem Link

Description

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The array-form of an integer num is an array representing its digits in left to right order.

• For example, for num = 1321, the array form is [1,3,2,1].

Given num, the array-form of an integer, and an integer k, return the array-form of the integer num + k.

 

Example 1:

Input: num = [1,2,0,0], k = 34
Output: [1,2,3,4]
Explanation: 1200 + 34 = 1234

Example 2:

Input: num = [2,7,4], k = 181
Output: [4,5,5]
Explanation: 274 + 181 = 455

Example 3:

Input: num = [2,1,5], k = 806
Output: [1,0,2,1]
Explanation: 215 + 806 = 1021

 

Constraints:

• 1 <= num.length <= 104
• 0 <= num[i] <= 9
• num does not contain any leading zeros except for the zero itself.
• 1 <= k <= 104

Solution

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Python3

class Solution:
    def addToArrayForm(self, num: List[int], k: int) -> List[int]:
        N = len(num)
        carry = k
        i = N - 1
        res = []
 
        while i >= 0 or carry > 0:
            if i >= 0:
                carry += num[i]
                i -= 1
 
            res.append(carry % 10)
            carry //= 10
        
        return res[::-1]