Add to Array-Form of Integer — LeetCode 989 Python Solution

The problem

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].

Example

Input

num = [1,2,0,0], k = 34

Output

[1,2,3,4]

Explanation

1200 + 34 = 1234

Python solution

class Solution:
    def addToArrayForm(self, num: List[int], k: int) -> List[int]:
        ans = []
        i = len(num) - 1
        while i >= 0 or k:
            k += 0 if i < 0 else num[i]
            k, x = divmod(k, 10)
            ans.append(x)
            i -= 1
        return ans[::-1]

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 989. Add to Array-Form of Integer is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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