LeetCode 989. Add to Array-Form of Integer

Description

https://leetcode.com/problems/add-to-array-form-of-integer/

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

Example 4:

Input: num = [9,9,9,9,9,9,9,9,9,9], k = 1
Output: [1,0,0,0,0,0,0,0,0,0,0]
Explanation: 9999999999 + 1 = 10000000000

Constraints:

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

Explanation

Convert the list to integer and plus it with k to get a sum. Then append all the digits of the sum to get a list.

Python Solution

class Solution:
    def addToArrayForm(self, num: List[int], k: int) -> List[int]:
        num_integer = 0
        
        for n in num:
            num_integer = num_integer * 10 + n
            
            
        sum_num = num_integer + k
        
        if sum_num == 0:
            return [0]

        results = []
        

        while sum_num > 0:
            results.append(sum_num % 10)
            sum_num = sum_num // 10

        return results[::-1]
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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