【Leetcode】Merge Two Sorted Lists (2 lists)

题目要求合并两个排好序的链表，这道题和add 2 number 思路比较类似，都是构造一个helper，然后把满足条件的NODE一个个往上添加

这道题注意的是指针的移动。不要忘记移动runner指针。

代码如下

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode helper = new ListNode(0);
ListNode runner = helper;
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
runner.next = l1;
runner = runner.next;
l1 = l1.next;
} else {
runner.next = l2;
runner = runner.next;
l2 = l2.next;
}
}
if (l1 != null)
runner.next = l1;
if (l2 != null)
runner.next = l2;
return helper.next;
}