LeetCode-Easy刷题(6) Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

合并两个排序链表，并将其作为一个新列表返回。新的列表应该通过将前两个列表的节点拼接在一起。

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

ListNode helper = new ListNode(0);//始终是总表的头部
ListNode pre = helper;//指针控制向前插入 相对参考系l1
pre.next = l1;

while(l1!=null && l2!=null){

if(l1.val>l2.val){
//将l2最前面节点解耦插入链表移动位置指针后
ListNode next = l2.next;
l2.next = pre.next;
pre.next = l2;
l2 = next;
}else{
l1 = l1.next;//移动参考系指针
}
pre = pre.next;
}

if(l2 !=null){
pre.next = l2;
}

return helper.next;
}

class ListNode {
int val;
ListNode next;
ListNode(int x) { val = x; }
}