合并排序链表

将两个升序链表合并为一个新的升序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

双指针遍历比较

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var mergeTwoLists = function(l1, l2) {
    let root = new ListNode()
    let cur = root
    while(l1&&l2){
        if(l1.val>l2.val){
            cur = cur.next = l2
            l2 = l2.next
        }else{
            cur = cur.next = l1
            l1 = l1.next
        }
    }
    l1&&(cur.next=l1);
    l2&&(cur.next=l2)
    return root.next
};