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 contain a single digit. Add the two numbers and return it as a linked list.

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

Examples:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

Solution

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
  // 创建链表作为返回值
  let res = new ListNode(0)

  let temp = res
  // 进位
  let carryBit = 0
  while(l1 || l2) {
    // 取链表节点值
    let n1 = l1 ? l1.val : 0
    let n2 = l2 ? l2.val : 0

    // 值相加
    let sum = n1 + n2 + carryBit

    // 相加结果大于10, 进位取1
    carryBit = sum >= 10 ? 1 : 0
    temp.next = new ListNode(sum % 10)
    temp = res.next

    l1 = l1 ? l1.next : l1
    l2 = l2 ? l2.next : l2
  }
  if (carryBit === 1) {
    temp.next = new ListNode(1)
  }
  return res.next
};