LeetCode 989: Add to Array-Form of Integer Solution

Master LeetCode problem 989 (Add to Array-Form of Integer), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

989. Add to Array-Form of Integer

Easy

Array Math

Problem Explanation

Explanation:

To solve this problem, we can simulate the addition process of adding the number k to the array-form of the integer num from right to left. We start by adding k to the last digit of num, then propagate any carry to the next digit until there are no more digits in num or no more carry.

Algorithm:

Initialize a variable carry to 0 to store the carry during addition.
Iterate through the digits of num from right to left.
Add the current digit of num with the corresponding digit of k and the carry.
Update the current digit of num to be the sum of the three values mentioned above.
Update the carry to be the floor division of the sum by 10.
If there are no more digits in k, break out of the loop.
If there are no more digits in num but there is still a carry, continue adding the carry to the remaining digits of k.
Reverse the updated num array to get the correct array-form of the sum.

Time Complexity:

The time complexity of this algorithm is O(max(N, log(K))), where N is the number of digits in the array num and K is the value of k.

Space Complexity:

The space complexity of this algorithm is O(max(N, log(K))) to store the result array.

Solution Code

import java.util.LinkedList;
import java.util.List;

class Solution {
    public List<Integer> addToArrayForm(int[] num, int k) {
        LinkedList<Integer> result = new LinkedList<>();
        int i = num.length - 1;
        int carry = 0;
        
        while (i >= 0 || k > 0 || carry > 0) {
            int sum = carry;
            if (i >= 0) {
                sum += num[i];
                i--;
            }
            if (k > 0) {
                sum += k % 10;
                k /= 10;
            }
            result.addFirst(sum % 10);
            carry = sum / 10;
        }
        
        return result;
    }
}

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