js链表——力扣刷题

/**
 * Definition for singly-linked list.
 * 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) {
    if (l1.val == 0 && l1.next === null) return l2
    if (l2.val == 0 && l2.next === null) return l1

    var x,y = 0;
    var head = new ListNode(0);
    let ptr = head;

    while(l1 || l2){
        x = l1.val + l2.val + y;//这步至关重要的，本次运算值包含三个部分  加数  被加数  进位值   注意进位值需记录
        y = parseInt(x/10);
        ptr.val = x%10;
    
        if (l1.next === null && l2.next === null && y != 1) return head;
        if (l1.next === null) l1.next = new ListNode(0);//高位添零
        if (l2.next === null) l2.next = new ListNode(0);

        ptr = ptr.next = new ListNode();
      
        l1 = l1.next;
        l2 = l2.next;

    }
};