2.Add Two Numbers.md

2.Add Two Numbers

Medium

https://leetcode.com/problems/add-two-numbers/

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.

Example:

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

与 21.Merge Two Sorted Lists 类似，都是单向链表

/**
 * 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) {
    var list = new ListNode(null)
    var head = list
    var sum = 0
    var carry = 0
    while(l1 || l2 || sum > 0) {
        if(l1) {
            sum = sum + l1.val
            l1 = l1.next
        }
        if(l2) {
            sum = sum + l2.val
            l2 = l2.next
        }
        if(sum >= 10) {
            carry = 1
            sum = sum - 10
        }
        head.next = new ListNode(sum)
        head = head.next
        
        sum = carry
        carry = 0
    }
    return list.next
};