LeetCode-in-All

2. Add Two Numbers

Medium

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]

Output: [7,0,8]

Explanation: 342 + 465 = 807.

Example 2:

Input: l1 = [0], l2 = [0]

Output: [0]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]

Output: [8,9,9,9,0,0,0,1]

Constraints:

Solution

import com_github_leetcode.ListNode

/*
 * Example:
 * var li = ListNode(5)
 * var v = li.`val`
 * Definition for singly-linked list.
 * class ListNode(var `val`: Int) {
 *     var next: ListNode? = null
 * }
 */
class Solution {
    fun addTwoNumbers(l1: ListNode?, l2: ListNode?): ListNode? {
        val dummyHead = ListNode(0)
        var p = l1
        var q = l2
        var curr: ListNode? = dummyHead
        var carry = 0
        while (p != null || q != null) {
            val x = p?.`val` ?: 0
            val y = q?.`val` ?: 0
            val sum = carry + x + y
            carry = sum / 10
            curr!!.next = ListNode(sum % 10)
            curr = curr.next
            if (p != null) {
                p = p.next
            }
            if (q != null) {
                q = q.next
            }
        }
        if (carry > 0) {
            curr!!.next = ListNode(carry)
        }
        return dummyHead.next
    }
}