LeetCode Entry

989. Add to Array-Form of Integer

15.02.2023 easy 2023 kotlin

use linked list to add to the front of the list in O(1)

989. Add to Array-Form of Integer easy

blog post

    fun addToArrayForm(num: IntArray, k: Int): List<Int> {
        var carry = 0
        var i = num.lastIndex
        var n = k
        val res = LinkedList<Int>()
        while (i >= 0 || n > 0 || carry > 0) {
            val d1 = if (i >= 0) num[i--] else 0
            val d2 = if (n > 0) n % 10 else 0
            var d = d1 + d2 + carry
            res.addFirst(d % 10)
            carry = d / 10
            n = n / 10
        }
        return res
    }

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Intuition

Iterate from the end of the array and calculate sum of num % 10, carry and num[i].

Approach

• use linked list to add to the front of the list in O(1)

  Complexity

• Time complexity: \(O(n)\)
• Space complexity: \(O(n)\)