[LeetCode] 2. Add Two Numbers

Description

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:

• The number of nodes in each linked list is in the range [1, 100].
• 0 <= Node.val <= 9
• It is guaranteed that the list represents a number that does not have leading zeros.

My Solution

function ListNode(val, next) {
  this.val = val === undefined ? 0 : val;
  this.next = next === undefined ? null : next;
}
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function (l1, l2) {
  let carry = 0;
  let dummyHead = new ListNode();
  let currentNode = dummyHead;
  while (l1 || l2) {
    const x = l1 ? l1.val : 0;
    const y = l2 ? l2.val : 0;
    const sum = carry + x + y;
    if (sum > 9) {
      carry = 1;
    } else if (carry === 1) {
      carry = 0;
    }
    currentNode.next = new ListNode(sum % 10);
    currentNode = currentNode.next;
    if (l1) l1 = l1.next;
    if (l2) l2 = l2.next;
  }
  if (carry === 1) {
    currentNode.next = new ListNode(carry);
  }
  return dummyHead.next;
};

Time complexity

• Best case: O(max(m,n))
• Worst case: O(max(m,n))
• Average case: O(max(m,n))

Space complexity

• Best case: O(max(m,n))
• Worst case: O(max(m,n))
• Average case: O(max(m,n))

Feedback

• 간단한 링크드 리스트 구현과 연산 문제이다.
• 자바스크립트에서는 링크드 리스트를 Node class나 consturctor functions로 구현해야 한다.
• LinkNode class

class ListNode {
  constructor(val = 0, next = null) {
    this.val = val;
    this.next = next;
  }
}

• 상속 등 객체 지향적인 설계를 하고 싶다면 class를 쓴다.