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. Note that need to especially handle the case when the sum value is 0.

Python Solution

class Solution:
    def addToArrayForm(self, num: List[int], k: int) -> List[int]:
        
        
        num_value = 0
                
        for val in num:            
            num_value = num_value * 10 + val
                
        sum_value = num_value + k
        
        if sum_value == 0:
            return [0]
        
        results = []
        while sum_value > 0:            
            results.insert(0, sum_value % 10)            
            sum_value = sum_value // 10
        
        
        
        return results
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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